LAMELLIBRANCHIATA. 445 



Beaks sub-central, prominent, rising above the hinge-line. Umbonal fur- 

 row oblique, broad and strongly marked. 



Surface marked by fine concentric striae, which are sometimes fasciculate, 

 as shown on the cast of the interior. 



A specimen has a length of 48 mm. and a height of 43 mm. 



This species is distinguished by its large size, prominent beaks, and broad 

 defined umbonal furrow. 



Formation and localities. In the sandstones of the Chemung group, at Kirk- 

 wood, Broome county, and Lindley township, Steuben county, N. Y. 



Paracyclas erecta, n. sp. 



PLATE XCV, FIG. 22. 



Shell of medium size, rhomboid, sub-elliptical ; height one-fifth greater than 

 the length. Anterior margin regularly curving, from the beaks to the post- 

 basal extremity, which is slightly produced. Posterior margin vertical. 

 Cardinal line short. 



Valves moderately convex below, becoming somewhat gibbous in the 

 umbonal region. 



Beaks sub-central, small, but little elevated above the hinge. Umbonal 

 slope obtusely sub-angular, extending to the post-inferior extremity. 



Surface marked by fine concentric striae which, toward the anterior and 

 basal margins, are fasciculate. 



The cardinal margin, in the cast, is marked by two slender ligamental 

 grooves, diverging from behind the beak. 



A specimen has a length of 20 mm. and height of 25 mm. 



This species is unlike any other in its erect form, vertical posterior margin 

 and defined umbonal ridge. The umbonal ridge gives the fossil the aspect of 

 ScHizoDUS, but the shell is more delicate than in the species of that genus, the 

 hinge is shorter, the beaks small and appressed, and the diverging grooves, 

 along the cardinal line are similar to Paracyclas. 

 57 



