CRETACEOUS FOSSILS. 135 



ovate, considerably wider towards the ventral margin tnan near 

 the dorsal, but slightly emarginated by the encroachment of 

 the preceding volution. Surface marked by simple, straight, 

 rounded ribs, arising on the umbilical margin, and continuing 

 over the dorsum. 



Septum composed of a dorsal, a superior and an inferior lateral, 

 and two supplementary lobes to the umbilical margin. Dorsal 

 lobe divided for half its length, deeply notched over the siphuncle, 

 each branch tridentate on the end, carrying one compound and 

 two simple spurs on the outer side ; body of the lobe bearing 

 two large spurs and one smaller one above. Dorsal saddle broad 

 and divided into two compound bifurcate branches. Superior 

 lateral lobe as long as the dorsal, narrow and bifurcate in the 

 middle, each branch being trifurcate on the end, and carrying 

 one large spur above on the outer side; body of the lobe with 

 two or three smaller spurs above. Lateral saddle like the dorsal, 

 but a little more simple. Inferior lateral lobe shorter than the 

 superior, divided a little below the middle into one complex 

 branch on the ventral side, and two more simple ones towards the 

 dorsal ; above this division is a large transverse spur on each side. 

 Inferior lateral saddle small and deeply bifurcate. First supple- 

 mentary lobe small, bifurcate, the lower branch tridentate ; the 

 remaining lobe consists of but three small spurs. 



From the Shasta Group, Cottonwood Creek, Shasta County. 

 Diameter, 4.25 inch ; diameter of umbilicus, 1.6 inch ; height of aperture from 

 top of inclosed volution, 1.8 inch ; greatest width, 1.8 inch. 



" A. Stoliczkanus, n. s. 



PI. 23, Fig. 16, a. 



Shell thick, robust, heavily costate ; whorls five or six, increas- 

 ing rapidly in size, enveloping nearly one-half of the preceding 

 volution; sides arched, most prominent in the middle, or a little 

 nearer the umbilical than the dorsal margin; back broadly 

 rounded, nearly flat; umbilicus large and deep, the umbilical 



