394 
PALAEONTOLOGY OF NEW-YORK. 
Cryptonella rectirostra. 
PLATE LXI. 
Terebratula rectirostra : Hall, Thirteenth Report on the State Cabinet,, p. 88. 1860. 
“ “ Id. Referred to Cryptonella 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 convex, 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 muscular 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. 
