QUADRULA 925 
Unio affints Hrupe, Conch. Fluv. Nank.. I, 1875, pl. 1, figs. 
7) 74. 
Quadrula similaris SIMPSON, Syn., 1900, p. 799. 
In the shell figured by Heude there are strong, corrugated 
ridges in the umbonal region running nearly parallel to the 
dorsal edge of the shell. The author’s specimen in the Nation- 
al Museum collection is somewhat eroded in this region, but 
does not seem to have these plications very much developed 
and I am not certain that it has been accurately named. It is 
close to microsticta, but is rather shorter, less decidedly rhom- 
boid and is not so finely sculptured. I am doubtful if the two 
are distinct. ‘The valves of this species and microsticta are 
scarcely, if at all, twisted. 
The name affinis was used long before by Dr. Lea for a 
Unio. 
QUADRULA MicRosticta (Heude). 
Shell subrhombcid, scarcely inflated, inequilateral, solid; 
beaks only moderately full and high, placed at some distance 
from the anterior end; posterior ridge full, rounded; anterior 
end rounded; base line curved, sometimes having a light sinus 
in front of the posterior ridge; outline of the dorsal slope 
curved, sometimes raised into a low angle behind the liga- 
ment ; surface, except the anterior portion, covered with strong 
nodules; dorsal slope having heavy, curved, corrugated ridges ; 
epidermis dark brown or blackish; pseudocardinals striate 
but not much split; laterals short, heavy, vertically striate, 
that of the right valve partly double; beak cavities very deep, 
compressed; anterior scars partly filled with rough nacre; 
nacre white, polished behind. 
Length 80, height 63, diam. 34 mim. 
China. 
Unio microstictus Heupr, Conch. Fluv. Nank., II, 1877, pl. x11, 
fig. 24. 
Quadrula microstictis StmPSON, Syn., 1900, p. 799. 
The epidermis is quite dark, the outline is rather rhomboid, 
the inflation is moderate and the ridges on the posterior end 
are numerous and strong. 
