Geol.— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. 105 



Chico beds of that place, the larger one being about thirty- 

 two centimeters in diameter, but not altogether perfect. 



The types of this species are in the collections of the 

 California Academy of Sciences. 



50. Pachydiscus sacramenticus, sp. nov. 



Plate VI, Figs. 133-134; Plate X, Fig. 195. 



Shell discoidal, not compressed, of moderate size; section of whorl sub- 

 elliptical, truncated at umbilicus, rounded sides sloping very gently to meet 

 rounded ventrum; umbilicus wide, walls sloping steeply, involution covering 

 one-half of inner whorls; surface marked by narrow, sinuous ribs curving 

 gracefully forward in crossing ventral surface, most prominent at two-thirds 

 distance from umbilicus to siphonal plane; ribs separated by wide grooves, 

 which do not extend to umbilicus, and diminish on ventral surface; minor 

 lines abundant between larger ribs; body chamber occupying two-thirds of 

 entire outer whorl, increases but gradually in size with age; ratio of umbilical 

 dimension to diameter thirty-three one hundredths; width of whorl eighty- 

 four one hundredths of depth; suture of large whorl not seen. 



This shell Dr. Stanton thinks is a Pachydiscus, and 

 the suture, so far as it can be seen, agrees with that 

 determination. 



Occurrence. — The species belongs apparently to the 

 upper portion of the Horsetown. The type was obtained 

 upon an east branch of Hulen Creek, Shasta County, Cal- 

 ifornia. Another smaller specimen, thought to be identical 

 with this one, was found at Horsetown. 



The type of the species is in the collections of the Uni- 

 versity of California. 



51, Sonneratia stantoni, sp. nov. 



Plate III, Figs. 91-93. Plate X, Fig. 198. 



Shell small, not often above a diameter ot 3.5 cm., discoidal, laterally com- 

 pressed and flattened; sides converging gently toward the periphery; ventral 

 surface rounded or subquadrate; umbilicus not large, less than one-third the 

 total diameter, generally funnel-form, owing to its sloping sides and the 

 increasing thickness of the shell; surface ornamented with about thirty 

 transverse flexuous ribs which usually cross the ventral surface and ter- 

 minate in about half as many distinct tubercules upon the shoulder of the 

 umbilicus. The ribs show a tendency to bifurcate from these ridge-like 



