3SG PALiEONTOLOGY OF NEW-YORK. 



GEXI'S TEREBRATITLA (Llhwyd, 1696). 



Among the fossils of the Upper 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 jiossible 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 a condttion to show the loop or internal structure, and we are usually 

 forced to rely upon external form and the muscular inapressions of the 

 casts, N 



In consequence of the finely punctate character and terebratuloid form 

 of l.hese shells, I refer them, with little hesitation, to the Family Tere- 

 bratulid^ ; and while some of them are known to be true Terebratul^ 

 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 them are known to possess the short terebratu- 

 loid loop. 



Terebratula lens. 



PLATE LX. ^ 



Tirebratula lent : Hall, Thirteciitli Report on thn 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- 



