TRILOBITES, &c.

Thename of this genus is derived from a Greek word which signifiesobscureorconcealed. The fossil animals included by it are characterized as having contractile bodies; the buckler as bearing many tubercles or folds—the cheeks as being oculiferous, and the abdomen and tail as being composed of from twelve to fourteen articulations or joints, without any membranaceous expansion. The Calymenes in thickness are nearly semicylindrical, and the buckler in front presents achaperonor upper lip more or Jess raised. In perfect specimens, there is a small furrow which seems to indicate a separation between the upper and under parts of this kind of lip. The eyes are always raised, and frequently present the remarkable structure observable in many of thecrustacea; but as this part is generally very prominent, thereticulationsof the eye are commonly worn off or injured.

Professor Brongniart places but little confidence in any of the generic characters above enumerated, except the number of articulations of the abdomen:these, however, in our opinion, are more vague and uncertain than most of the others. The genus, however, we think may be readily identified, after becoming familiar with one well characterized species. The general aspect of the buckler is peculiar—the body is not so depressed as in most other genera, and the lateral lobes are destitute of all membranaceous expansion.

To the genus Calymene, belongs the celebrated Dudley fossil, calledEntomolithus paradoxusby Blumenbach, but which is not the same organic relic, to which Linné applied that name.

This genus includes a great number of species, and though some of them are said to be found in different and distant parts of the globe, they are according to our limited observation, for the most part confined, like recent species of animals, to particular districts. The C. polytoma, C. pulchella, C. bellatula, C. concinna, C. sclerops, and the C. punctata, all finely figured by Professor Dalman, and which are found in Sweden, have not yet been noticed in any part of North America.[12]

[12]See the valuable and extensive communication of J. W. Dalman, M. D., on the Trilobites, in the Transactions of the Swedish Academy for 1820, part 2d.

Clypeo rotundato, tuberculis sex distinctis in fronte; oculis in genis emintissimis; corpore tuberculato.

In this species the upper lip presents a furrow parallel to its edges. The lip is straight. The cheeks are a little projecting. There are six rounded tubercles on the front, and fourteen articulations on the back; the tail is small, and the shell is covered with small rounded tubercles of unequal sizes.

The above is Professor Brongniart's description of this trilobite, which is the famous Dudley fossil described and figured by Littleton, in the Philosophical Transactions, (London) in 1750. According to Dalman, several distinct European species have been published under this name. The true C. Blumenbachii, he says, has thirteen articulations to the abdomen, and about eight to the tail. In the cabinet of G. W. Featherstonhaugh, Esq., we have examined a fine perfect specimen from Dudley,[13]in which there is fourteen abdominal joints. There can be no doubt, however, that several species have been confounded under the name of C. Blumenbachii; Dalman's C. Tuberculata and C. Pulchella are, we think, distinct from it, though he has marked them only as varieties.

[13]This famous trilobite, once formed a part of the cabinet of Mr. Parkinson, the distinguished author of the "Organic Remains," and is accurately figured on one of the plates of that splendid work. At the sale of the late Mr. Parkinson's fossils, it was purchased by Mr. Featherstonhaugh,

The true C. Blumenbachii, no doubt, abounds in North America, and is one of the few examples of the occurrence of an identical species on both continents. The late Abbe Correa sent a perfect specimen to Brongniart, from the vicinity of Lebanon, in the stateof Ohio. We have also seen a number of specimens from that state, which could not be distinguished from the Dudley trilobite. Our model was taken from a specimen found at Trenton Falls, in the state of New York.

The three following species found in the United States, will no doubt be considered by many as mere varieties of the C. Blumenbachii; we have ventured, however, to call them by distinct names.

[14]From two Greek words, which signify "beautiful head."

Clypeo antice attenuato, figura liliiformi in fronte depicta; oculis minimis; abdomine quatuordecim articulis; corpore plano.

The buckler is subtriangular; on the front there is a figure in high relief, somewhat resembling afleur de lis; or perhaps more, the capital of a Corinthian column. The oculiferous tubercles are rather lower down on the cheeks than usual. The articulations of the abdomen and the tail cannot well be distinguished from each, other; fourteen in all may be easily counted. The middle lobe of the abdomen is nearly equal in breadth throughout. The ribs, or costal arches, are not grooved or bifurcated at their extremities. Length nearly two inches and a half.

This beautiful species is in the Philadelphia Museum, where it is labelled as being found in "Hampshire, Virginia." It is mineralized by a dark yellowishlimestone. It differs from the C. Blumenbachii, in the form and number of its articulations; in the shape of the head; in having only two flat tuberculous elevations on the front; and in other particulars.

In the cabinet of the New York Lyceum, and in that of J. P. Wetherill, Esq. there are some examples of this species from the Miami river, near Cincinnati, Ohio. I have also seen it from Indiana, in a dark coloured limestone, very much distorted. It has never been found at Trenton falls, or at any other locality, as far as my knowledge extends, which yields the true C. Blumenbachii.

[15]From the Greek for "lunate head."

Clypeo antice rotundato, margine omni valde incrassato; prominentia frontali utrinque trituberosa; corpore tuberculato.

The buckler is regularly lunate; the margin is slightly reflected or raised anteriorly, the posterior edge forms a continuous rim, running nearly parallel with the articulations of the abdomen. The front on each side has one large and two small tubercles, near its superior edge. The oculiferous tubercles on the cheeks are on a line with the lowest frontal tubercle. There are fourteen distinct articulations; but as the tail is mutilated and distorted, the total number of joints cannot, from this specimen, be ascertained. The body appears to have been covered with smallpustules. These are very evident on the front. Costal arches simple, or not grooved. Length, one inch and three-fourths, breadth of the buckler one inch and one-fourth.

This species resembles a little the C. Pulchella of Dalman. The specimen from which the model was taken, is in the possession of Mr. R. Peale, of New York, who willingly lent it for this monograph. He informed me that it was found in the state of New York, but he was unable to name its precise locality. It occurs in a soft ash coloured limestone. No other petrifaction is observable in the fragment of rock which contains it.

[16]From a Greek word which signifies Flat,

Clypeo antice rotundato; prominentia frontali utrinque quatuor tuberculis.

The buckler is probably semilunate; but as the anterior portion is lost, this cannot be determined with precision. The posterior raised rim is not continuous, as in the C. Selenecephala, but is separated by the longitudinal dorsal furrows. The front is distinctly divided from the cheeks, and has four tubercular prominences on each side. Three of them are nearly on a line with the lateral edge of the cheeks, and gradually diminish in size, as they descend to the anterior part of the buckler. The other is smaller, and is between, and a little to the side, of the uppertwo. The cheeks form spherical triangles. The oculiferous prominences are close to the second large tubercle on the front. The cheeks are, however, quite imperfect. The articulations of the back cannot be distinguished from those of the tail. In our specimen they are all beautifully distinct, and are twenty-two in number. The posterior raised rim of the buckler seems to form an articulation; its extremities on each side are a good deal thickened and expanded. The costal arches suddenly curve downwards and backwards, near their middle, so as to divide the abdomen and tail into five unequal sections. The whole length is nearly three inches. The breadth of the buckler nearly two inches.

This fine large Calymene was accidentally discovered on the Helderberg mountain, by my friend, Professor T. R. Beck. One of the loose pieces of sandstone rolling over, near his feet, presented him the fine natural mould, from which he has kindly permitted our cast to be taken. The animal relic once enclosed in this matrix, must still be near that locality, and yet remains undiscovered, to reward the enterprise of some more fortunate naturalist.

One of our models represents the natural mould found by Dr. Beck. The other is a cast taken from it and exhibits, more satisfactorily, the various parts of the animal.

[17]From the Greek for "small eyes."

Clypeo antice subattenuato; occulis minimis in lateribus capitis; abdominis articulis a 14 ad 18; corpore depresso.

The buckler is semi-elliptical, slightly punctate, and much depressed anteriorly; the front and cheeks are not very distinctly marked. The eyes are very remote from each other, being situated near the posterior lateral angles of the head. They are not very prominent, and exhibit no marks of being reticulated. Before the eye on each side, there is a slight transverse indentation. It is difficult to distinguish the articulations of the abdomen from those of the tail. They are from fourteen to eighteen in number. Where the lateral lobes remain perfect, two narrow raised lines appear between each of the ribs; these are most evident on the caudal extremities of the animal. The middle lobe is in the form of a long, slender, and acute cone. The whole animal is an inch and a quarter long, and is much more depressed than any other Calymene which we have seen.

I am indebted to Mr. Titian R. Peale for the use of the original from which our model was taken, his liberality to those who cultivate Natural History is proverbial, and needs no encomium from me. The C. Microps is said to have been found near Ripley, Ohio. It occurs in black limestone.

The eyes of this Calymene are small in comparisonwith those of some other species—particularly the C. Bufo, C. Macrophthalma, and C. Anchiops.

[18]From two Greek words which signify "eyes approximate."

Clypeo antice, caudaque postice rotundatis; oculis approximis, magnis, excertis; articulis vigenti; corpore plano.

The buckler of this species is irregularly hemispherical; the front pyriform and without pustulations. The cheeks are almost entirely occupied by the eyes, which are placed very near each other on the upper part of the forehead; are very large and trilobate, the side lobes being elongated and attenuated in front. The articulations of the back are twenty in number, those of the abdomen not being distinguishable from those of the tail. The costal arches of the side lobes are round near their extremities, and are intersected with two or three raised lines. Length nearly four inches. Breadth about two inches.

It gives me great satisfaction in being able to describe, and to present to naturalists a good cast of this Calymene, which has excited for a long time so much interest and perplexity. The original fossil from which our plaster model was made is now deposited in the cabinet of the Albany Institute, and is the identical specimen from which a cast was long since made, by Dr. Hosack of New York, a specimenof which he sent in July, 1819, to the Royal Academy of Science, in France. Professor Brongniart referred the animal from which this model was taken, though with much hesitation and doubt, to the species, Calymene Macrophthalma. He remarks concerning it, "Il est beaucoup plus gros que les autres individus, et a prés de dneuf centimètres de longueur. C'est avec doute que je rapporté cette empreinte tres-peu nette à l'espèce actuelle; mais malgré ses formés obtuses, et l'absence de tout detail, elle est si remarquable par la grosseur de ces yeux et par le prolongement de son bouclier qu'on peut présumer qu'elle appartient an calyméne macrophthalme, et avec d'autànt plus de probabilité qu'elle vient aussi des Etats Unis d'Amérique. Elle a été trouvée, suivant M. Hosack, dans un schiste." We have seen the cast alluded to in the above note, and are not at all surprised at the uncertainty which it has occasioned. The apparent prolongation of the buckler is entirely occasioned by the loss of a small fragment from that portion of the head. The form and position of the eyes, further distinguish it from any of the numerous specimens of C. Macrophthalma, that we have examined. The raised lines which we have noticed as intersecting the costal arches of the lateral lobes are remarkable, though they may have been produced by accidental fissures in the epidermal covering of the animal. The head of the C. Macrophthalma is always marked by minute and prominent granulations, likeshagreen—nothing of this kind appears on the buckler of the C. Anchiops.

I am informed by my friend, Dr. T. R. Beck, to whose liberality I owe this interesting species, that it was found in Ulster county, New York. It was supposed by Dr. Hosack, to have been discovered in the vicinity of Albany. Respecting the locality and geological relations of this trilobite, Professor Brongniart remarks, "un modéle en plâtre de trilobite envoyé à l'Académie des Sciences, en Juillet, 1819, par M. Hosack, et que j'ai rapporté, autant que la chose était possible, et toujours avec doute, au calyméne macrophthalme, a été trouvé dans le territoire d'Albany, êtat de New York. Or, les environs de cette ville sont indiqués, sur la carte géologique de M. Maclure, comme formés de terrains de transition. M. Hosack dit qu'il a été trouvé au milieu d'un rocher ardoisé, c'est à dire, dans un schiste probablement analogue à celui des environs d'Angers, qui renferme les Ogygies, et ce trilobite ce rapproche un peu de ce genre par la grosseur des tubercules qui recouvrent les yeux on en tiennent la place." The rock in which the Calymene Anchiops is found, appears to be a clay slate.

[19]From the Greek for "Double Eyes."

Clypeo lobato plano; rugis tribus in lateribus frontis; tuberculis oculiformibus, eminentissimis et duplicibus; articulis octodecim; cauda rotunda.

This species is very distinct from every other Calymene that we have seen. The outline of the buckler islobate lunate; the front is very convex, and a good deal elevated above the cheeks or sides, from which it is divided by a deep furrow; on the posterior margin of the front on each side, close to the groove there is a prominent circular tubercle, before which there are three small transverse wrinkles. The cheeks are subtriangular; the oculiform tubercle is near the posterior superior angle, and is only separated from the tubercle on the front, by the furrow or groove, so that the animal seems to have had double eyes on each side; there are two curved lines on each side below the eyes, crossed near the front by a deep short canal. The middle lobe of the abdomen and tail is rather longer than the lateral lobes, and is rounded and very prominent throughout. It is composed of 18 articulations, seven of which appear to belong to the tail; it is, however, somewhat difficult to define the length of the tail with precision. The costal arches of the lateral lobes, particularly those near the tail, are bifurcate. Length almost three inches.

The original fossil, from which the cast was taken, is in the New York Museum. I am indebted to Mr. Rubens Peale, the liberal proprietor of that flourishing and important institution, not only for the use of it in this Monograph, but also for some valuable information relating to other species. The precise locality of Mr. Peale's specimen is not known, but in the cabinet of J. P. Wetherill, Esq., there is a fine head of the C. diops which was found in the State of Ohio. Both specimens are mineralized by the same kind of soft grey coloured limestone—and I havebut little doubt that they were derived from the same place.

[20]From the Greek for "Great eyes."

Clypeo antice, caudaque postice attenuatis, oculis magnis exsertis.

This species, according to Al. Brongniart, who first described it, is remarkable for the magnitude and protuberance of its eye-shaped tubercles, and by the prolongation of the anterior portion of the buckler, in the form of a snout.

The back is marked by 12 or 13 articulations, which are thicker than those of the tail. The tail is short, pointed, and without expansion.

The middle lobe, or front of thebuckler, in this calymene, is said by Brongniart to be marked on its sides by three oblique plicæ or wrinkles, but we have not been able to discover this character in any of the specimens to which we have access; neither do they exhibit any remarkable prolongation in the anterior portion of thebuckler, as stated in his specific character. The specimens which we have examined, agree pretty well with the representation he has given of the C. Macrophthalma, Plate I. fig. 5. A. B. & C. made from a drawing by Mr. Stokes, from a fossil found in Coalbrookdale (Eng.).

This trilobite is common in several parts of theUnited States. According to Dr. J. E. Dekay,[21]the C. Macrophthalma is found on the Helderberg mountains, near Albany, and at Coshung creek, not far from Seneca lake, in the State of New York. It occurs also at Leheighton, in Pennsylvania—at the Falls of the Ohio, and at several other localities. We have examined a number of specimens of the C. Macrophthalma, contained in the rich cabinet of fossils, in the Academy of Natural Sciences, and have never seen any individual which resembles the fig. 4, Plate I. of Brongniart; and in no instance is the front of the buckler marked by three oblique folds, a character stated as peculiar to this species. The C. Macrophthalma, (variety) occurs in large quantities in Leheighton in Pennsylvania, and we are indebted to Mr. D. Keim, for some fine specimens from that locality.

[21]See Annals of Lyceum, Vol. I. p. 188.

The authority of Professor Brongniart is sufficient to place the C. Macrophthalma among the species of the United States, though we have been unable fully to identify it with his description.[22]He received aspecimen, transformed into red jasper, from Prof. Ducatel, said to be found in the United States—no precise locality is given. Our model represents the animal which is supposed to be the one intended by Brongniart as the C. Macrophthalma of North America. It is, in our opinion, a variety of the C. Bufo. There can be no doubt that several species have been confounded under the name of C. Macrophthalma.

[22]We have seen in the Cabinet of Mr. Featherstonhaugh, a fine group of trilobites, in the transition limestone, from Dudley, (Eng.) Among them there is a perfect head, which agrees exactly with the description given by Mr. Brongniart of the head of his Calymene Macrophthalma. If this belongs to the true macrophthalma, our species under that name is entirely distinct. Since our work had been prepared for the press, Dr. J. J. Cohen, of the Baltimore College, has shown us the fragment of a calymene from Berkley, Virginia, which agrees with Brongniart's description of the macrophthalma, and with the above fossil from Dudley. We regret that the imperfection of the fossil prevents our giving a satisfactory cast of it.

The following extract of a letter from Professor Ducatel to the author, referring to the locality of this species, will be read with interest.

"I cannot be positive as to my recollection of the locality of the fossil referred to by Brongniart and yourself, but believe it is one of several found by my friend Dr. M'Culloh, in the neighbourhood of Berkley Springs, Virginia. I regret that I have not in my possession another specimen to present to you."

Clypeo rotundato, convexo, punctato; abdominis articulis sexdecim; cauda attenuata; corpore plano.

Buckler semilunate, front very large, rounded before and arcuated at the insertion of the middle lobe; surface convex, and marked with numerous depressed pimples. Mouth large, lunate, resembling that of atoad or frog, with a narrow raised rim on the upper and under lip. Below the chin there are no pustulations. Cheeks small, triangular, and separated from the front by a deep, rectilinear furrow; the eyes in our specimen are much injured, but they are large, and near the upper angle of the cheeks. Middle lobe with a series of distinct double articulations. Lateral lobes wider than the middle lobe, ribs deeply grooved near their insertion; articulations of the abdomen twelve; of the tail ten. Length four inches and a half; breadth of the buckler nearly two inches.

This fossil was presented to me some time since by Thomas P. Johnson, Esq., who mentioned that it was found in New Jersey, but that he could not learn its precise locality. Near Patterson, in that State, some trilobites have been discovered—perhaps the C. Bufo may have been derived from that locality. It is composed of a dark greyish limestone, easily cut with a knife.

This fine specimen differs from the one above described, in having the front of the buckler rather smaller, and of a different contour. The whole of the shell is also covered with granulations, which only appear on the head of the other; this, however, may be only an imperfection in the specimens in our cabinet.

I am indebted to the Albany Institute for the originals of the models Nos. 11 & 12. They were found atSeneca, Ontario County, New York, in dark, slaty limestone, which also contains cubical crystals of iron pyrites. A fortunate blow of the hammer has fractured the rock which contains this trilobite, so neatly, as to present us at the same time with the petrified animal in an almost perfect state, and also with the mould or matrix in which it was imbedded. This arrangement is beautifully illustrated by our models.

Genus Asaphus.Brongniart.

This genus derives its name from the Greek word Ασαφης—obscure. It embraces perhaps more species than any other genus of the family of trilobites. About twenty have already been discovered. Most of them are very characteristic and can easily be determined, but as the genus Asaphus, is intermediate between Calymene and Ogygia, it is sometimes a little difficult to decide the genus to which the inosculating species on each side, belongs.

In general, the Asaphs may be known by the body being very much depressed, and by the membranaceous development, which extends beyond the lateral lobes. The middle lobe of the abdomen, is rarely more than one-fifth the width of the body. As the abdomen and tail of the Asaph are the only portions of the animal commonly found entire, the distinctive characters of the genus above given, may generally be ascertained.

Professor Brongniart remarks, that the ribs of theAsaph, which correspond in number and position tothe articulations of the middle lobe, "are sometimes simple or undivided, at least in the post abdomen, but that they are always bifurcated in theCalymene" As far as our observations have extended, these remarks do not apply either in the one case or the other.

The head or buckler of theAsaph, is not so deeply divided into three lobes as theCalymene; they are, however, quite distinct. The oculiferous tubercles are in some species exceedingly well marked by a reticulated structure.

This genus often occurs at the same localities with the Calymene, though in some instances it seems to occupy rocks peculiar to itself. Dr. John Bigsby, in his list of organic remains occurring in the Canadas, states, that he never found a single species of the genus Calymene, on the north side of the River St. Lawrence, although the Asaphs were very abundant.[23]In his Sketch of the Geology of the Island of Montreal, he however observes: "Of Trilobites, the Asaph genus is the most abundant, they approach nearest the speciescaudatus, of Brongniart. I have found no entire Calymene, but many bucklers or heads of the Blumenbach species, some of them an inch and a half in diameter. They are found whole in considerable numbers in the vicinity of Quebec."[24]

[23]Silliman's Journal, vol. viii. p. 83.

[24]Annals New York Lyceum, vol. i. p. 214.

[25]From the Latin for "broad ribbed."

Cauda prælonga, pars ad marginem vix membranacea; cute coriacea, tuberculis minimis; costis latis, convexis et valde distinctis.

The fragments of this species, which we have examined, comprise ten articulations of the middle lobe, and the corresponding ribs of the sides, all in a very good state of preservation; the extent to which the membranaceous expansion reached beyond the tail and the lateral lobes is very apparent, but it has been unfortunately broken off all round. Our specimen appears to be a natural cast of the internal part of the shell, or the coriaceous covering of the animal.

The portion of this specimen of trilobite which still remains perfect, is two inches long, and three inches and a quarter broad. The middle lobe exhibits the appearance of a very exact and gradually tapering cone, its articulations being rounded and slightly flattened on the top. The ribs of the lateral lobes are nearly straight, slightly arched, broad, rounded, and gradually increase in width from the point of their insertion; they are simple or not bifurcated throughout, and are covered with very minute granulations, which are probably produced by the sandstone in which the animal is mineralized. The membranaceous expansion near the caudal termination, is a good deal prolonged.

The A. Laticostatus occurs in a light colouredferruginous sandstone, which contains a multitude of other fossil remains, particularly a large species of Productus and of Terebratula. It is said to have been found in Ulster county, in the State of New York, by the late Charles Wilson Peale, Esq., the distinguished founder of the Philadelphia Museum. During the memorable search after the bones of theMastodon Giganteum, in the marl pits of that county, this enterprising naturalist procured our Asaph with many other remarkable petrifactions. The rocks which contain them were probably found notin situ, but were masses rolled from the neighbouring Shawangunk mountains,[26]which by some geologists are supposed to be a link in the grand chain of the Alleghanies. Mr. R. Peale, of New York, lately visited the rich repository of fossils in Ulster County, and procured a number of specimens of the A. Laticostatus, all of which he has kindly permitted me to examine. These are much smaller than our cast, but in many instances the caudal elongation is perfectly developed. The A. Laticostatus also occurs in the Helderberg mountains, specimens of which are in the Albany Institute.

[26]The Lenape tribe of Indians, who formerly inhabited this district of country, gave the name of Shawangunk to this stupendous ridge of hills a name which has been very properly preserved.

[27]Derived fromSelene, moon, andouros, tail.

Cauda semilunari; costis angustis, valde distinctis; abdominis articulis duodecim; corpore convexo.

I am indebted to Professor Eaton, for two specimens of this very interesting species. In his Geological Text Book, he thus describes it: "Tail crescent-form, or concavo-convex, with the convex side forward, upon which the post abdomen terminates: abdomen contains about 12 articulations, with an abrupt termination equal in breadth to one-fourth of the length of the transverse lunate tail; the articulations of the side lobes gradually incline towards the axis of the body, until the last pair terminate at the tail. Found in transition limestone at Glenn's Falls, and Becroft's mountain, near Hudson. I have a specimen from Becroft's mountain, with part of the original covering of the animal remaining."

When we first noticed the remarkable lunate appearance of the tail of this Asaph, we supposed that it was occasioned by some accident, but there seems no doubt that this conformation is natural. In our specimens of this species, which are not however perfect, the articulations of the abdomen do not exceed 8 in number. The representation of this animal remain given by Mr. Eaton, plate 1, figure 1, is exceedingly inaccurate; it will confuse rather than illustrate the subject. Our cast and the drawing, we believe, are taken from the same specimen, which was kindly loaned by Mr. Eaton for this work. It is but justice to the amiable, industrious, and indefatigable author of the Geological Text Book to remark, that he regrets as much as any one, the insufficiency of his figures of the trilobites, to give any correct idea of the fossils they are intended to represent.

In the cabinet of the Albany Institute there are a number of specimens of the A. Selenurus. One of our models represents the natural mould made by the animal in the rock; the other is an impression taken from it, in order to exhibit the animal in a more satisfactory manner.

[28]From two Greek words, which signify "Limulus tailed."

Cauda longa, spina munita sicut in Limulo; costis abdominis in spinis retrorsum flexis, desinentibus.

It is very much to be regretted that the abdomen and caudal end only of this remarkable Asaph have hitherto been discovered; it is, however, exceedingly gratifying that the fragment still remains in so perfect a state. It forms a part of the magnificent cabinet of organic remains belonging to J. P. Wetherill, Esq., now deposited in the Academy of Natural Sciences, of Philadelphia.

Dr. J. J. Cohen discovered a small specimen of this species at Lockport, New York, which he has presented to the Athenæum, in Baltimore.

Eight articulations of the abdomen, and ten of the tail, are all of this fine species that we have seen. The ribs, or costal arches of the abdomen have a deep furrow on their upper surface, commencing at the middle lobe, and terminating near their free extremities; these extremities appear all detached from each other, and end in reflected points or spines, so asto give the side of the animal a serrate appearance. The costal arches of the tail are grooved through their whole extent, and present no spinous terminations. Beyond the membranaceous expansion of the tail, which is somewhat similar to that of the Asaphus Caudatus, there projects a single spine, like that from the tail of theLimulus polyphemus; this spine may be traced under the caudal membrane to its insertion into the middle lobe. A portion of the crustaceous shell is still entire, and it seems to have been covered with very minute granulations. A row of large granulations may easily be traced on each side of the middle lobe. Length of the fragment, one inch and a half. Breadth one inch and a fourth.

The A. Limulurus was found in the dark brown, shaly limestone, at Lockport, in the State of New York; it is associated in the same rock with the terebratula and several other fossils.

The singular spinous projection from the tail of this Asaph, furnishes another analogy, between the trilobite and the limulus; an affinity which was suggested by Dr. Dekay; and which has been argued with great ingenuity both by himself and Professor Wahlenberg.[29]

[29]See Nova Acta Regiæ Societatis Upsalensis: 1821. Also, Annals of the Lyceum of Natural History. New York. Vol. i. pages 179-185.

[30]From the Latin word for "tailed,"

Clypeo antice subrotundato, postice valde emarginato, angulo externo in mucronem producto; oculis exsertis, conicis, truncatis, distincte reliculatis; post abdomine in caudam membranaceam, acutam extenso. (Vide Brongniart.)

The middle lobe of the buckler is marked by three transverse plicæ or folds on its posterior part, and its cheeks or lateral portions are triangular; the posterior exterior angles of which, are acute, and considerably elongated. The cheeks are furnished with conical, truncated, semilunar and externally convex tubercles, which were beyond all doubt the eyes of the animal, being reticulated as in those of the Limulus. The middle lobe of the back is narrow, and has twelve articulations. The lateral lobes are composed of double ribbed costal arches. Beyond the lateral lobes and the caudal termination, there is a smooth, thick membranaceous expansion, which forms an acute projection below the central portion of the tail.

The specimen in the Philadelphia Museum, by which I have identified this species, is marked as coming from Ripley, Ohio. It reposes on a fragment of ash coloured limestone—which contains also a mutilated specimen of what seems to be a calymene, and a few small terebratulæ, &c.

Dr. John Bigsby, in his "List of Organic Remains, occurring in the Canadas," states that the A. caudatus is frequently met with, thrown up by the water on the north shore of Lake Superior—on the bank of Rainy river—at the Lake of the Woods, and at several other places. In some localities they are astonishingly numerous, and so small as to be almost microscopic. They occupy indiscriminately limestone of every colour, but are most numerous in that which is brown or crystallized. They are composed of the kind of limestone in which they happen to be embedded.

We have seen a number of specimens of this species in the Albany Institute, in Mr. Wetherill's cabinet, and in the Baltimore Athenæum; but in all of them, the abdomen and caudal extremity only remain perfect: from their exact resemblance, however, to the same parts of the A. caudatus, figured by Brongniart, (plate 2, fig. 4, D.) we have no hesitation with regard to their identity. The description which we have given of thebuckler, supposed to belong to our Asaph, is therefore taken from Brongniart, whose specimens were found at Dudley, the celebrated locality of the C. Blumenbachii.[31]The coriaceous membrane, which extends beyond the lateral lobes and forms the caudaltermination of our species, is not covered with minute dots, as in the European fossil; and if a new name is to be applied to it on that account, it may be calledA. glabratus.[32]M. Wahlenberg, has given the figure of a trilobite which he callscaudatus, but ours cannot be mistaken for that species, to which Brongniart has very judiciously applied the name ofA. meucronatus.

[31]In the first volume, 2d series, of the Transactions of the Geological Society of London, Mr. Weaver has published some highly interesting observations on the fossils found in Gloucestershire, England. The A. caudatus, he states, is there found in the transition limestone, though very much mutilated. (Vide p. 326.)

[32]In the cabinet of G. W. Featherstonhaugh, Esq., I have examined a fine specimen of the A. caudatus, from Dudley, England, but could not perceive the minute dots on the tail, as mentioned by Brongniart.

The conical eye-like protuberances on the head of this species, are very remarkable, and so much resemble the reticulated eyes of the limulus, as to leave no doubt that they once contained the organs of vision.

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