CKETACEOUS FOSSILS. 415 



Genus SPHJCRIOLA. 



SPHiElilOLA TRANSVERSA. 



Plato 10, figs. 14-lG. 



Sphcvriola transversa Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 'M. 



Shell of rather large size, subspheroidal, a little transverse, or, longer 

 than high exclusive of the projection of the beaks, the outline of the 

 margin of the valve being slightly oblate or transversely broad-oval, and 

 nearly symmetrical. Valves highly inflated on the central area and uni- 

 bones, with strong, highly elevated, strongly incurved, subcentral beaks, 

 which are slightly curved forward and subangular on the umbonal ridges. 



Surface of the shell marked by sublamellose concentric lines of growth, 

 which form strong distant undulations in some cases toward the extremities 

 of the shell. 



Internally the muscular impressions are large and subcircular, and 

 the pallial line simple and entire. The cardinal teeth, as obtained bv a 

 gutta-percha mold from a natural cast, consist of two tuberculiforni teeth 

 beneath the beak, and the laterals are represented by a strong oblique fold 

 or ridge, passing from near the beak to within a short distance of the pos- 

 terior border of the hinge plate, where it is marked, or divided, by an 

 impressed pit, which may be accidental. 



Compared with ^S*. obliquata Meek, this shell is more equilateral, the 

 beaks more nearly central, and the shell less oblique. It differs from S. 

 moreamnsis of the same author in having much larger beaks, which are 

 more strongly enrolled and the shell is also more transverse. 



Formation and locality. — In ferruginous sandstone of Cretaceous No. 

 5, on the Cheyenne River, near Old Woman Fork, Wyoming. 



