﻿IIYKIOI'STS 207- 



Genus HYRIOPSIS Conrad, 1853. 



Ilyriopsis Conrad, Pr. Ac. N. Sci. Phila., 1853, p. 269. 



Shell large, compressed, rhomboid-elliptical, dorsally winged 

 and generally biangulate behind, sometimes produced in the 

 post-basal region ; beaks low, mostly compressed, the sculpture 

 consisting of numerous concentric ridges, which are nearly 

 parallel with the growth lines, generally extending well on to 

 the disk of the shell, the earlier ones fine, often slightly nodu- 

 lous or doubly looped ; epidermis olive to brown, sometimes 

 faintly rayed ; pseudocardinals two or three in the left valve, 

 one to three in the right, when young compressed, but often 

 breaking into irregular denticles when old ; laterals long, com- 

 pressed, two in the left valve and one in the right, sometimes 

 vertically striate, the left valve often having a sort of raised 

 lamellar tooth at or just behind the beak. Beak cavities shal- 

 low ; dorsal scars numerous, extending from the cavity down- 

 ward and forward. Anterior muscle scars three, distinct, pos- 

 terior large, indistinct ; front end of the shell usually thickened : 

 a row of plications often occurring just below the laterals, a"^ 

 in Crist aria. 



Animal unknown. 



Type, Unio delphinus Gruner. 



Group of Hyriopsis hialata. 



Shell somewhat trapezoidal, with a posterior ridge, biangu- 

 late behind, with a very high, pointed, triangular, posterior 

 wing, and a smaller, pointed one in front, which projects for- 

 ward ; beaks low, sculpture not seen ; epidermis brown ; pseudo- 

 cardinals broken up into denticles ; hinge line slightly curved ; 

 the three anterior muscle scars separate and deep ; dorsal scars 

 not extending greatly downward in front ; nacre bluish-white. 



Hyriopsis bialata Simpson. 



Shell elongated, subrhomboid, with a high, triangular pos- 

 terior wing and a smaller anterior one, these wings are gen- 

 erally broken off when the shell becomes old ; subsolid. rather 

 compressed ; posterior ridge high, angular, with a faint sec- 



