20 University of Michigan 



Pleurohema vwculatmn (Con.), Simpson, "14, p. 727 

 Pleurobema conradi Vanatta, '15, p. 559. 



Lexingtonia dolahclloides conradi (Van.), Ortmann, '18, p. 546. 

 Pleurobema conradi. Van., Walker, 'i8c, p. 172. 



The new name conradi has been properly introduced by 

 Vanatta to take the place of the preoccupied maculatus Con. 



If the two forms are to be regarded as varieties of the same 

 species, which is not determined here, dolabelloides as the 

 oldest valid name is that of the main species ; while conradi 

 is that of the variety. The earlier name maculatus Con. must 

 not be considered. 



Genus Pleurobema Rafinesque, 1819 



Type: Pleurobema mytiloides Raf., '20= Unio clava 

 Lam., '19. 



Pleurobema Rahnesque, "19, p. 427; '20, p. 313 (no type named). 



Hermannsen, '47, p. 292 (type, Unio mytiloides Raf. = Unio clava 

 Lam.) ; Agassiz, '52, p. 49; Simpson, 'OQf, p. 745, and '14, p. 7:^2. 



Scalenaria Rafinesque, '20, p. 309 (no type named) ; Herrmannsen, 

 '48, p. 422 (type, Unio scalenius Raf.). 



In his original description of Pleiiroheinu (1819) Rafinesque 

 cited two undescribed species, mytiloides and comccii' The 

 latter never was described, so that if the former can be rec- 

 ognized, Avhen subsequently described, it ipso facto became 

 the type, the genus being monotypic. 



Pleurobema (1820) was founded upon two species, myti- 

 loides and cuneata; both are surely U. clava Lam. (which see). 

 Herrmannsen designated U. m.ytiloides Raf., which was unnec- 

 essary if our position that Pleurobema is really monotypic is 

 correct. If not, his was the first designation of a type for the 

 genus. Agassiz took up Rafinesque's generic name, but with- 

 out naming a type. Since, however, mytiloides (== clava) is 

 the only species of Rafinesque included in the original diag- 

 nosis, this becomes the type. Thus. Simpson was justified on 



