F. ozarkensisCall, Pr. U. S. Mus. 10, ’87, p. 499, pl. 27. Tr. St. Louis Ac. 7, ’95, p. 33, pl. 18.Lampsilis ozarkensisMeek & Clark, Bur. Fisher. Doc. no. 759, ’12, p. 18.Pleurobema utterbackiFrierson, in: Utterback, Naiad. Missouri (Amer. Midland Natural 4, 1916, p. 86, pl. 5, pl. 20, f. 63).
I have specimens from James River, Galena Stone Co., Mo., and White River, Cotter and Norfolk, Baxter Co., Ark., donatedby L. S. Frierson and collected by A. A. Hinkley on July 30 and Aug. 2 and 5, ’14, A number of specimens (8) were preserved in alcohol, coll. July 30 and Aug 2, which all were gravid females, and one of each date had glochidia. This marks probably the end of the breeding season, and the species is tachytictic.
There is some confusion with regard to this species. After the first description by Call, it has not again been recorded, except by Meek and Clark, and I believe, the identification of these authors (supported by B. Walker) is correct. But I think that other authors have seen this form, but have not recognized it, and, for instance, Simpson’spannosusandsubellipticus(regarded as varieties ofPleurobema argenteumandbreverespectively) are also this. Frierson’sutterbackiis surely this, since my specimens were thus labeled by Frierson.
Walker, Frierson, and Simpson (in part) believe this to be aPleurobema, and not aLampsilis(see also Simpson, ’00, p. 557, and ’14, p. 131), and this comes nearest to the truth, in fact, it is the most plausible assumption to be made from the study of the shell alone. The shell “resembles a very elongatedQuadrula coccinea,” according to Meek and Clark, and the comparison withPleurobema argenteumandbreve(which, by the way, are synonyms), made by Simpson, is significant. We must keep in mind that Call’s fig. 4 represents the normal shape of the shell, while his fig. 1 is rather abnormal, and possibly does not belong here at all. These two figures by no means represent the female and male, as Call believes.
The investigation of the soft parts has shown that this actually is aFusconaia. Corresponding, both in soft parts and shell, to thebarnesiana-type of the upper Tennessee region.F. ozarkensisdiffers frombarnesianaby the more elongated (subtrapezoidal) outline of the shell, more anterior beaks, and the weak development of the rays, which are faint at the best, and often entirely absent. A swollen form of it is not known to me, but specimens from White River are slightly more convex than those from James River (farther up). Also Utterback’s quotation of Frierson (p. 87, footnote) make it probable that there are differences in obesity.
Anatomy.
Supraanalopening probably separated from theanalby a short mantle-connection, but in all my specimens this is torn by rough handling. Inner lamina of inner gills free from abdominal sac. All four gills marsupial in the female.Placentaewell developed andsubcylindrical.
Anal opening with small papillae, branchial opening with well developed papillae.Palpias usual, their posterior margins connected for about one third of their length or less.
As to the color of the soft parts, which is so characteristic inbarnesiana, not much can be said, since my material has been too long in alcohol. But in most of my specimens the gills are yet distinctly suffused with black. The placentae have been rendered whitish, but here and there traces of a dark stain are preserved (which is disappearing gradually). It is quite possible that the color of the placentae originally was similar to that ofbarnesiana.
Theglochidiaare subelliptical, slightly higher than long; L. O. 15, B. O. 18, thus agreeing with those ofF. barnesiana.