No. 186.J 97 



CLIODERMA CANALICULATA (n.s.). 



Shell subovate, triangular, subarcuate ; the sides nearly straight, 

 or sometimes a little concave from the apex to the middle 

 of the shell or below : apex moderately incurved. Dorsum 

 abruptly and strongly carinate from the apex ; the carina 

 gradually expanding towards the front, which is deeply 

 sinuate : ventral partition extending more than halfway from 

 the apex to the front. Interior cavity shallow, modified by 

 the form of the carina. Surface marked by flattened lamellose 

 striae, which are parallel to the margin and abruptly arching 

 backwards on the carina. 



In the best preserved specimens there is a shallow groove or depres- 

 sion parallel to the lateral margins, and apparently along the line of 

 junction between the outer shell and the partition; but as none of the 

 specimens are entire, the relations of this feature are not fully deter- 

 mined. 



CLIODERMA UNDULATA ( n. s.). 



Shell sub circular or broadly subelliptical, moderately and 

 equally convex ; length and width about as eleven to twelve ; 

 margin curved from the apex, and broadly rounded in front ; 

 apex short, and but moderately incurved ; central carina un- 

 known ; the ventral partition extending more than half way 

 from the apex to the front of the shell, but apparently uniting 

 with the shell considerably within the lateral margins ; visce- 

 ral cavity very shallow. Surface marked by strong concentric 

 undulations, with finer parallel striae. 



This species is distinguished from the two preceding by its nearly 

 orbicular form, little extension of apex, rounded postero-lateral margins, 

 and broad undulations of surface. 



Geological formation and locality. In Trenton limestone : at Water- 

 town, N. Y. 



[Assembly, No. 136.] 13 



