LAMELLIBRANCHIATA OP THE LOWER MARLS. 49 



greatest width of the shell. Auriculations of nearly equal size, but only 

 moderately large, the posterior side on the left valve gradually receding 

 toward the hinge and the anterior one on the same valve sloping in the 

 opposite direction. Cardinal slopes of the body of the shell slightly con- 

 cave. Left valve marked by from thirty to thirty-five narrow, raised, but 

 slender flattened ribs, with broad flattened interspaces, often six or eight 

 times as wide as the ribs. Ribs increased by intercalations, never by bifurca- 

 tion. General surface of the left valve marked by very fine, raised con- 

 centric lines, which are regularly and evenly arranged but scarcely per- 

 ceptible to the unaided eye. Interior of the shell showing very faintly the 

 lines of the ribs. Right valve unknown. 



In its narrow flattened ribs with wide interspaces this species differs 

 conspicuously from any other species described from the green marls of 

 New Jersey or elsewhere. It presents the general form and proportions of 

 Camptonectes Burlingtonensis Gabb; and were it not for the fact that Mr. Gabb 

 has figured both valves of that species and shown them to be destitute of the 

 strong radiating ribs, I should have been inclined to have considered it as the 

 left valve of that species As yet I have only observed the left valve, and am 

 inclined to expect a right valve very similar to that of (7. Burlingtonensis. 



Formation and locality. — In the dark-blue marls of the Lower Green Sands, 

 at G. C. Schanck's pits, near Marlborough, New Jersey. 



Pecten (Chlamys) craticulus. 

 Plate VII, Figs. 17 and 18. 



Pecten craticula Morton. Synopsis, p. 57. Gabb, Synop., p. 158. Meek, Check-list, 

 p. 7, Geol. Surv. N. J., 1868, p. 725. 



Dr. Morton's type specimen of this species consists of a fragment rep- 

 resenting about one-third of one valve. It is a moderate-sized species and 

 possesses very strong rounded ribs, probably ten or twelve in number, the 

 interstices being occupied by a single smaller rib. The ribs, both large 

 and small, are marked on their surfaces b}^ comparatively coarse striations, 

 eight or nine of them on each large rib, and a fewer number on the smaller 

 ribs and interspaces. Strong concentric lines cross the ribs and form rugae 

 or granules at their junction with the striations. Toward the margin there 

 4418 MON 9 4 



