320 PALAEONTOLOGY OF NEW YORK. 



abruptly rounded at the posterior extremity. Cardinal line declining from 

 the beaks in both directions. Anterior end sloping rapidly from the beaks 

 and rounded below ; posterior end longer and more pointed. 



Valves convex, gibbous in the umbonal region. 



Beaks usually at about the anterior third, sometimes sub-central, short, 

 mo<lerately elevated, brosid and slightly incurved. Umbonal slope not dis- 

 tinctly defined, rounded, direct, extending to the post-basal extremity. 



Surface marked by very fine concentric striae, and by irregular varices of 

 growth, which sometimes produce strong undulations in the surface of the 

 shell. 



The post-cardinal teeth are large and strong, contrasting with the preced- 

 ing species, N. varicosa. 



Three specimens measure respectively 17, 16 and 14 mm. in length, and 

 12.5, 12 and 9 mm. in height. 



This species is distinguished by its sub-equilateral triangular form. 



Formations and localities. In the shales of the Hamilton group, on the shores 

 of Cayuga, Seneca and Canandaigua lakes ; and a single doubtful specimen from 

 the Chemung group, of Ithaca, N. Y. 



NUCULA LAMELLATA. 



PLATE U, FIGS. 18-21i PLATE XLV, FIG. 13; AND PLATE XCIII, FIG. 7. 



Xwtila laiaellata. Hall. Pal. N. Y., vol. v. pt. 1. Plates and Explanations : PL hi, tigs. 18-21. 1883. 



Shell small, elongate-ovate, truncate behind ; length twice the height ; basal 

 margin broadly curving, straight, or slightly arcuate in the middle ; poste- 

 rior margin short, obliquely truncate. Cardinal line straight, directed some- 

 what upward toward the anterior. Anterior end large and regularly 

 rounded. 



Valves gibbous, with a broad flattened depression extending from the beaks 

 to the base and sometimes slightly constricting the margin. 



Beaks sub-central or posterior to the middle of the shell, incurved, rising 

 a little above the hinge-line. Umbo gibbous. Umbonal slope obtusely sub- 



