LAMELLIBRANCHIATA. 397 



The identification with Mr. Conrad's species was made from a lithographed 

 figure which has never been published. 



Formation and locality. In the shales of the Hamilton group, in Schoharie 

 county, N. Y. 



Sphenotus subtoktuosus. 



PLATE LXV, FIGS. 18, 19. 



Sangui7u>lite.i subtortvosux, H.KLL. Prelim. Notice Lamellibi-anchiata, 2, p. 41. 1870. 



" " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations: PI. 65, tigs. 18, 19. 



1883. 



Shell largc,^ robust, trapezoidal ; length more than twice the height ; basal 

 margin constricted anterior to the middle /ind gently curving to either 

 extremity. Posterior extremity doubly truncate. Cardinal margin straight 

 or gently arcuate, and very slightly declining posteriorly. Anterior end 

 short, abruptly declining from the beak and narrowly rounded below. 



Valves moderately convex posteriorly, becoming gibbous in the middle 

 and umbonal region. 



Beaks sub-anterior, attenuate, appressed and incurved, rising but little 

 above the hinge-line. Umbonal slope marked by a low ridge, extending to 

 the post-inferior extremity, becoming undefined below the middle of its 

 length. Post-cardinal slope convex, marked along the middle of its width 

 by a low ridge, extending from the beaks to the posterior extremity, produc- 

 ing an angularity in the margin. Cincture broad, distinct, extending from 

 the beaks and constricting the basal margin a little anterior to the middle. 



Surface marked by fine concentric striae, which in some parts of the shell 

 are fa.sciculate, producing low undulations of the surface ; Jind also by fine 

 radiating striae, which are often not well-preserved. 



Ligiimental area narrow ; characters of the interior unknown. 



Two specimens measure respectively 50 and 55 mm. in length, and 23 and 

 26 mm. in height. 



This shell resembles the preceding, but is a larger and more robust form, the 

 valves are more gibbous ; the umbonal ridge is distinctly arcuate, not so 



