Occasional Papers of the Museum of Zoology 9 
Genus PLECTOMERUS Conrad, 1853 
Type: OU, trapezoides Wea. 
Bariosta Rafinesque, ’31, p. 2 (type, U. ponderosus Raf.) ; Frierson, 
PLA vaDat 7 
Plectomerus Conrad, ’53, p. 260 (no type named). 
The U. trapezoides has been placed in Crenodonta (cor- 
rectly Amblema, which see) by Simpson (’0o°) and Ortmann 
(12), but after the restriction of this genus to the species of 
the type of A. costata (with beak sculpture not extending upon 
the disk), it cannot remain in it. Utterback has created for 
gigantea Bar. (heros Say) the genus Megalonaias, but it does 
not appear safe to unite trapezoides with this, while the anat- 
omy of the female of trapezoides is incompletely known. 
The best way, for the present, is to introduce a separate 
genus for trapezoides (Lea). ‘Two names should be consid- 
ered in this connection. The first is Bariosta Raf. ’31, founded 
upon the single species ponderosus Raf. Frierson believes 
that this is the same as trapezoides Lea, but, as will be shown 
under trapegoides (which see), ponderosus is not recognizable 
and Bariosta is thus not available. 
The other name is Plectomerus Con. No type is given for 
this and about nine other species are assigned to it, all “plicate” 
forms, generally belonging to Amblema and Megalonaias. But 
among them is also Plect. crassidens Lam. (a) =U. trape- 
goides Tea, and thus it is admissible to restrict Plectomerus 
Con. to this species as type, and with it probably goes also U. 
sloatianus Lea ’40==atromarginatus Lea ’40 = plectophorus 
Con. ’50, also standing, as separate species, under Conrad’s 
Plectomerus. 
If trapezoides should finally prove to be congeneric with 
gigantea, Utterback’s Megalonaias (1916) would have to give 
way to Plectoimerus (1853). 
