894 PALEONTOLOGY OF NEW-YORK. 



Cryptonclla rectirostra. 



PLATE LXI. 



Terebratula rtctiroitra : Ball, Thirteenth Report on the State Cabinet,, p. 88. 1860. 



'• " Id. Referred to Crtptonella in Fourteenth Report, p. 101. 1861. 



Cryptonella rectirostra : Id. Sixteenth Report on the State Cabinet, p. 44. 1863. 



Shell elongate-ovate, subovate or elliptical ; the greatest width anterior 

 * to the middle : valves subequally conyex, rounded or subtruncate at 



the base. 

 Ventral valve regularly arcuate, most convex in the middle, sometimes 



a little flattened at the base : beak much extended beyond the oppo- 

 site valve, moderately incurved and truncated by a round foramen, 



which is completed on the lower side by two narrow deltidial pieces. 



Shell abruptly inflected from the umbonal slopes to the cardinal 



margin. 

 Dorsal valve scarcely more convex than the opposite, gibbous towards 



the umbo, and regularly curving to the base and baso-lateral margins ; 



beak closely incurved beneath the deltidial plates of the opposite 



valve. 

 Surface marked by fine concentric lines of growth, and often at some 



what regular intervals by imbricating lamellae. Structure finely 



punctate. 



In the dorsal valve, the musoular impressions are narrow and elon- 

 gate ; and in the ventral valve the teeth are strong, and the muscular 

 imprint elongate, with strong vascular markings extending nearly to the 

 base of the shell. The crura are extended below the middle of the length 

 of the shell and then abruptly recurved, reaching backwards more than 

 half way to the apex : the crural processes penetrate deeply into the 

 ventral cavity, and between these and their origin the crura are connec- 

 ted by a transverse band. 



This species varies from individuals of less than half an inch in length 

 to those of nearly an inch and a half. In the older shells, and sometimes 

 in the younger ones, the lamellose concentric lines are very conspicuous. 



