FOSSILS OF THE NIAGARA GROUP. 141 



squarely truncate, owing to the abruptly declining anterior portion of the 

 valves below the inflated umbonal region. 



Surface of the valves marked by moderately strong radiating costa3, 

 about seven or eight of which occupy the space of half an inch, meas- 

 ured near the middle of the basal border on the larger specimen. The 

 costse appear to have been low, rounded, simple, and with exceedingly 

 narrow interspaces. As far as can be determined from the specimens in 

 . their condition as casts, the costa) have been strongest on the middle of 

 the shell, becoming gradually finer toward the posterior portion of the 

 valves. 



Beneath the beaks in the casts is preserved the remains of what ap- 

 pears to have been the filling of a rather large, double depression in the 

 hinge plate of each valve, which may have been the cavity for the re- 

 ception of an internal ligament ; or it may have been a tooth and liga- 

 mental cavity in one, and tooth cavity and ligament in the other. This 

 feature has been observed in several specimens of other species, but has 

 always been a little obscure. If specimens were collected with a little 

 care, and examined in connection with the matrix, this question could 

 be readily determined. One of the individuals of this species examined 

 shows evidence of an anterior and posterior muscular imprint of medium 

 size ; the former situated near the anterior border of the shell, about 

 half way between the beaks and the basal line, the other just within 

 the margin of the shell, below the extremity of the hinge line — the two 

 being connected by a distinct and entire pallial line. 



Formation and locality : In limestones of the Niagara group, near the upper portion 

 of the formation (Guelph horizon), at Cedarville, Greene county, Ohio. Ohio State 

 collection. Collected by Prof. E. Orton. 



GASTEROPODA. 

 Genus SUBULITES (Hall), Conrad. 



(Pal. N. Y., Vol. I., p. 182, 1847.) 



SUBULITES TEREBRIFORMIS (ll. sp.). 



Plate 8, fig. 6. 



Shell of moderate size, elongate terebriform, spire not regularly taper- 

 ing, but verj'- slightly swelling along the middle to the center of the 

 body volution, from which point it is again contracted to the lower ex- 

 tremity. Spire consisting of four or five volutions, the last or body volu- 



