LAMELLIBRANCHIATA. 447 



SCHIZODUS, King. 1844. 



SCHIZODUS ? FISSA. 



PLATE LXXII, FIGS. 35-41. 



Paracyclasf fissa. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 72, fijfs. 35, 36. 1883. 

 elemta, " Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 72, figs. 37-41. 1883. 



Shell of medium size or larger, obliquely sub-ovate, or sub-trigonal ; length 

 greater than the height ; basal margin regularly rounded. Posterior extrem- 

 ity narrowly rounded below, and gently curving toward the beak. Cardinal 

 line short, about half the length of the shell. Anterior end short, regularly 

 rounded. 



Valves regularly convex below, gibbous in the middle and above. 



Beaks in advance of the anterior third, large, acute, prominent and but 

 little incurved in the cast. Umbonal slope arcuate, marked by a slight 

 depression. 



Surface of the cast marked by fine concentric striae. 



This species carries a distinct lunule and a deeply marked escutcheon. 

 The anterior nmscular impression is very strongly marked, situated close to 

 the anterior margin, immediately below the lunule. Posterior scar large, 

 shallow, situated on the post-cardinal slope, near the extremity. The cast is 

 distinctly marked by a groove, extending from the beaks obliquely backward 

 more than half way to the base in well-preserved specimens, and is much 

 more strongly marked on the beaks and upper part of the valve. 



Three specimens measure respectively 31, 34 and 40 mm. in length, and 

 28, 29 and 34.5 mm. in height. 



This species is referred with doubt to the genus Schizodus, since we have no 

 means of ascertaining the characters of the hinge. As compared with the species 

 of that genus, in the succeeding formations, it differs in the arcuation of the 

 cardinal line, and the narrow and rounded post-cardinal slope. A further 

 examination of the specimens shows that those heretofore recognized as two 

 species should be united under a single name. 



Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 



