38 University of Michigan 



name Lastena to this form (and imhecillis) is incorrect. If 

 imbecillis is to be separated from Anodonta, as Utterback pro- 

 poses, another name will have to be found. 



Genus Simpsoniconcha Frierson, 1914 



Hemilastena Simpson, '00c, p. 673, '14, p. 323 (type, ambigua Say) 

 (not Hemilastena Agassiz, '52; type, dehiscens Say=/cfa Rai.). 



Simpsonaia Frierson, '14", p. 7 (type, ambigua Say) (Nomen pr<e- 

 occupafum). 



Simpsoniconcha Frierson, '14c, p. 40 (type, ambigua Say) ; Walker, 

 'i8% p. 4, and "i8c, pp. 64, 178. 



Hemilastena Ag. is a synonym of Lastena Raf. (which see), 

 as pointed out by Frierson and Walker, thus a new generic 

 name for the one species (ambigua Say) belonging to it was 

 in order. 



Genus Alasmidonta Say, 1818 



Subgenus Decurambis Rafinesque, 1831 



Decitrambis Rafinesque, '31, p. 4; Frierson. '14^, p. 7. 



Rugifera Simpson, 'oo^', p. 670; '14, p. 504; Walker, 'i8p. p. 178. 



Type: Alasmodon (Decitrauihis) scriptiim Rai . = Alasmi- 

 donta marginata (Say). 



The validity of Decurambis depends on the recognition of 

 either of the two species originally attributed to it,Alasmodon 

 scriptum Raf. and atropurpnrcnm Raf. '31. As will be seen 

 under Alasniidonta marginata (Say), the former at least is 

 undoubtedly identical with this, which is the type of Simpson's 

 Rugifera. Thus Decurambis supersedes Rugifera. 



Al,ASMIDONTA ( DFXURAMBIS) MARGINATA (Say). 1819 



Type locality: Scioto River, Chillicothe, Ohio. 



Alasmodonta marginata Say, '19. 



Alasmodon {Decurambis) scriptum Rafinesque, '31, p. 4. 

 Alasmodon {Decurambis) atropurpnrcum Rafinesque. '31, p. 4. 

 A. marginata Say = ^. scriptum Raf., Conrad, '34, p. 72; Ferussac, 

 '35, p. 25. 



