Fusconaia ozarkensis (Call) 1887.
F. ozarkensis Call, Pr. U. S. Mus. 10, ’87, p. 499, pl. 27. Tr. St. Louis Ac. 7, ’95, p. 33, pl. 18. Lampsilis ozarkensis Meek & Clark, Bur. Fisher. Doc. no. 759, ’12, p. 18. Pleurobema utterbacki Frierson, 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., donated by 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’s pannosus and subellipticus (regarded as varieties of Pleurobema argenteum and breve respectively) are also this. Frierson’s utterbacki is surely this, since my specimens were thus labeled by Frierson.
Walker, Frierson, and Simpson (in part) believe this to be a Pleurobema, and not a Lampsilis (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 elongated Quadrula coccinea,” according to Meek and Clark, and the comparison with Pleurobema argenteum and breve (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 a Fusconaia. Corresponding, both in soft parts and shell, to the barnesiana-type of the upper Tennessee region. F. ozarkensis differs from barnesiana by 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.