Geol— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. 121 



grooves noticed in the preceding species. In development this species is 

 very similar to the preceding, but differs from it considerably in the adult 

 shells. The essential differences are: (i) the narrower umbilicus of S. inulti- 

 costa; (2) the fle.KUous ribs, which have a greater tendency to form tuber- 

 cules upon the umbilical shoulders from which bifurcate the ribs; and 

 (3) the absence of the grooves along the sides of the keel. The whorls are, 

 furthermore, usually inflated in the younger forms. 



Occurrence. — This species occurs abundantly at the 

 Smith Ranch, about two miles west of Phoenix, Oregon. 

 The horizon is that of the Forty-nine Mine, and is 

 the equivalent of the Lower Chico of the Sacramento 

 Valley. 



The types are in the collections of the California 

 Academy of Sciences. 



68. Schloenbachia bakeri, sp. nov. 



Plate II, Figs. 26-33. 



Shell discoidal, compressed, quadrilateral in section; umbilicus wide and 

 shallow, with rounded sides; keel prominent and entire, with slight grooves 

 along the sides; involution covering about one-third the inner whorl; sides 

 ornamented by about thirty-eight to forty-four simple, oblique ribs, which 

 are narrow and sharply angular, each extending from the inner margin of the 

 whorl to the keel. 



The ribs form only small tubercules upon the umbilical margin of the 

 whorl, though a few of them become a little more prominent here, while 

 near the periphery a double row of inconspicuous nodes occurs. The ribs 

 bend sharply forward as they approach the keel, while seen from the side 

 they appear straight for the greater part of their length. They begin to 

 form uniformly at 3>^ whorls at a diameter of 3 mm. 



Keel high and thin, with only faint undulations along its summit, some- 

 times not to be seen at all. The smallest coils of the shell are smooth, 

 without keel, and almost circular in section except for the impressed zone. 

 The keel begins to appear upon the third whorl at a diamet«r of between 

 2 and 3 mm. 



The diameter of the largest specimen found is a little more than 3 cm., 

 and this is probably the average diameter of adult shells. The body- 

 chamber occupies about two-thirds of the last whorl. 



Although a number of otherwise perfect specimens of 

 this species were found, the suture of an adult shell was 

 not seen. As far as could be ascertained, it is similar to 

 that of the following species, S. oregonensis, to which it is 

 related. 



