Occasional Papers of the Museum of Zoology 9 



Genus PlEctomERUs Conrad, 1853 

 Type: U. trapesoides Lea. 



Bariosta Rafinesque, '31, p. 2 (type, U. ponderosiis Raf.) ; Frierson, 

 '14% p. 7- 



Plectomcnis Conrad, '53, p. 260 (no type named). 



The U. trapezoides has been placed in Crenodonta (cor- 

 rectly Amblana, which see) by Simpson ('00**) and Ortmann 

 ('12), but after the restriction of this genus to the species of 

 the type oi 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 ponderosiis Raf. Frierson believes 

 that this is the same as trapezoides Lea, but, as will be shown 

 under trapezoides (which see), ponderosus is not recognizable 

 and Bariosta is thus not available. 



The other name is Pleotoinerus Con. No type is given for 

 this and about nine other species are assigned to it, all "plicate" 

 forms, generally belonging to Amhlema and Megalonaias. But 

 among them is also Pleat, crassidens Lam. (a) = U. trape- 

 zoides Lea, and thus it is admissible to restrict Plectomenis 

 Con. to this species as type, and with it probably goes also U. 

 sloafianiis Lea '4.0 = atromarginatiis Lea '40 = plectophonis 

 Con. '50, also standing, as separate species, under Conrad's 

 Plectomerns. 



If trapezoides should finally prove to be congeneric with 

 gigantea, Utterback's Megalonaias (1916) would have to give 

 way to Plectomerns (1853). 



