﻿252 MICDKIMDl'S 



Miiv'^aron (Tuio) ocutissiimis Li;.\, Syii.. 1852. \\ 21; 1870, 



P- 32. 

 Mcdiouidus aciitissiiiiiis v^imi'son, Syn.. 1900, p. SOO. 

 Unio scmiMicatiis KrsTi:,K, Conch. Cal). Tnio. 1862. p. 279. 



pi. xciv, fij^. 4. 

 f/w/o nihclliniis \j:.\. \'r Ac. .\. Sci. I'hila.. TX. 1857. p. 32; 



Jl. Ac. N. Sci. Phila., IV. 1858, p. 70. ])1. xiii. fii^. 51 ; Obs., 



\l, 1858, p. 70, pi. XIII. fig. 51. 

 Margaron (Unio) rubellinus Lk.\, Svn.. 1870, p. 32. 

 [7f«'o nibclliaiiiis ScuviCRin'. Condi. Icon., XX'f. 1868. pi. xc, 



fig. 490. 



Lea's Unio aciitissimus seems to be merely a young and 

 somewhat compressed form of rubellinus, which is adult and 

 considerably inflated. The species of this group are close 

 and often difficult to satisfactorily determine. This form is 

 more inflated and has a higher, sharper posterior ridge than 

 any of the rest, and the male is more decidedly arcuate. 



There is a Unio semiplicatus of Troschel in Wiegman's 

 Archiv. for 1841, p. 180, but I do not know what it is. Kuster 

 credits his species to Australia, but it is evidently Lea's shell, 

 no such species being found in Australia . 



Ciroup of Mcdionidns "a'alkcri. 



Shell rather short, inflated, with a high posterior ridge ; pos- 

 terior slope strongly corrugated : e])idcrmis dark, slightly 

 clouded ; nacre reddish or greenish. 



Mi^niONiDus wAi.KRRi ( B. H. Wright). 



Shell subrhomboid, rather short, solid, slightly inflated, with 

 a high, angled posterior ridge; beaks full, moderately high, 

 their sculpture not observed : posterior slope covered with radi- 

 ating, curved corrugations ; the remainder of the shell with 

 strong, irregular growth lines, sometimes feebly corrugated ; 

 epidermis dark, ai)parently unicolored, but when viewed by 

 transmitted light it is often clouded or s]:)otted, sometimes 

 having a few angular, dark spots, but never rayed ; left valve 



