FOSSILS OF THE NIAGARA GROUP. 151 



between the dorsal extremity of the aperture and the first septum on the 

 inner side of the shell ; the entire length of the aperture is equal to 

 about six-sevenths of the shortest diameter of the largest part of the 

 shell. Septa rather closely arranged, slightly concave, and strongly 

 arching upwards on the back, each of them, except that next the outer 

 chamber, marked near the upper margin, as seen in the portion of a cast 

 figured, by an impressed line to near the inner side, where it becomes 

 deflected from the direction of the septum, and crosses to its lower limits. 

 On the surface of the cast are seen distinctly depressed lines running 

 lengthwise, and corresponding to the curvature of the shell, giving evi- 

 dence of the exterior surface having been faintly lirated, or longitudin- 

 ally fluted. Siphuncle small, situated about twice its diameter from the 

 inner margins of the septa. 



This species has its nearest analogue in 0. se2Jtoris=Gomphoceras septoris, 

 Hall, 18th Rept. State Cab., p. 350, but differs in the greater length of the 

 outer chamber, in the form and proportion of the lobes of the aperture, 

 in the more lateral position of the opening, and in the rounding or 

 sloping of the ventral side of the outer chamber. The dorsal lobes of the 

 aperture in that species are seven, one being central and the other three 

 pairs gradually lessening in size towards the ventral side, while in this 

 there is no central one, and each of the others are of nearly the same 

 lateral extent. 



Formation and locality : In the limestones of the upper part of the Niagara group 

 (Guelph horizon), at Cedarville, Greene county, Ohio. Ohio State collection. Col- 

 lected by Rev. H. Hertzer. 



Genu-s PHRAGMOCERAS, Broderip. 

 Phragmoceras parvum (n. sp.). 



Plate 8, fig. 10. 



Shell small, strongly curved, and rapidly expanding toward the outer 

 chamber; transversely broadly ovate below, but becoming more flattened 

 toward the aperture ; widest on the dorsal side of the center, and rounded 

 on the back, the inner side narrow, and almost sub-angular. Outer 

 chamber about as long as the dorsoventral diameter of the shell at the 

 upper margin of the last septum ; edges of the aperture sharply inflected 

 toward each other, contracting the opening to a narrow slit along the 

 middle of its length, which terminates in a rounded triangular opening 

 at the dorsal end, the margins of which are slightly raised; and at the 



