386 
PALAEONTOLOGY OF NEW-YORK. 
Gems Terebratula (Llhwyd, 1696). 
Among the fossils of the Up^er Helderberg and Hamilton groups, 
several species present externally and internally the features of Tere¬ 
bratula. The shell-structure is punctate, the beak incurved and termi¬ 
nated by a round perforation, which is limited on the lower side by two 
deltidial pieces. In other species of punctate structure, there is a certain 
modification of muscular marking which has induced me to separate 
them from Terebratula, under the name Cryptonella. With our present 
knowledge of external forms and characters, it is not possible to distin¬ 
guish generically those with a short terebratuloid loop from such forms 
as Centronella julia, without knowing their internal structure ; while 
certain other forms, with flat or concave dorsal valve and punctate 
structure, we regard as congeneric with C. glans-fagea. Unfortunately, 
our specimens from the. Hamilton group, though numerous, are rarely 
in q condition to show the loop or internal structure, and we are usually 
forced to rely upon external form and the muscular impressions of the 
casts. 
In consequence of the finely punctate character and terebratuloid form 
of these shells, I refer them, with little hesitation, to the Family Tere- 
BRATULiDiE ; and while some of them are known to be true Terebratula: 
from their internal structure, others are referred to that genus from simi¬ 
larity of external form and character. Among the following species placed 
under this genus, four of theifi are known to possess the short terebratu¬ 
loid loop. 
Terebratula lens. 
PLATE LX. 
Terebratula lens : Hall, Thirteenth Report on the State Cabinet, p. 89. 1860. 
Shell ovate, broadly elliptical or lenticular below the beak, which is 
abruptly tapering; moderately gibbous, the valves subequally convex, 
the greatest width a little below the middle, the width about four- 
