38 University of Michigan 
name Lastena to this form (and imbecillis) 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, ’00°%, p. 673, "14, p. 323 (type, ambigua Say) 
(not Hemilastena Agassiz, 52; type, dehiscens Say = lata Rat.). 
Simpsonaia Frierson, ’14", p. 7 (type, ambigua Say) (Nomen pre- 
occupatum). 
Stmpsoniconcha Frierson, *14°, p. 40 (type, ambigua Say); Walker, 
78", p. 4, and “18°, 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 
Decurambis Rafinesque, ’31, p. 4; Frierson, *14*, p. 7. 
Rugifera Simpson, ’00°, p. 670; *14, p. 504; Walker, ‘18°, p. 178. 
Type: Alasmodon (Decurambis) scriptum Rat. = Alasmi- 
donta marginata (Say). 
The validity of Decurambis depends on the recognition of 
either of the two species originally attributed to it,dlasmodon 
scriptum Raf. and atropurpureum Raf. ’31. As will be seen 
under Alasuudonta marginata (Say), the former at least is 
undoubtedly identical with this, which is the type of Simpson’s 
Rugifera. Thus Decurambis supersedes Rugifera. 
ALASMIDONTA (DECURAMBIS) MARGINATA (Say), 1819 
Type locality: Scioto River, Chillicothe, Ohio. 
Alasmodonta marginata Say, ’19. 
Alesmodon (Decurambis) scriptum Rafinesque, °31, p. 4. 
Alasmodon (Decurambis) atropurpureum Rafinesque, ’31, p. 4. 
A. marginata Say = A. scriptum Raf., Conrad, ’34, p. 72; Ferussac, 
"35; D: 25. 
