122 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The name proposed for this species is borrowed from 

 the frontier history of Southern Oregon, old Fort Baker 

 having stood within a short distance of the locahty from 

 which the type was collected. 



Occurrence. — This shell is tolerably abundant at the 

 locality of the Forty-nine Mine, near Phoenix, Oregon, on 

 the horizon of the Lower Chico beds. 



The type is in the collections of the CaHfornia Academy 

 of Sciences. 



69. Schloenbachia oregonensis, sp. nov. 



Plate II, Figs. 48-57; Plate VI, Fig. 144; Plate VII, Fig. 149. 



Sehloenbachia oregonensis Anderson (M. S.), J. P. Smith, Jour. Morph., 

 Vol. XVI, 1899, p. 10, Pis. A-E. 



Shell discoidal and compressed, increasing in thickness with age; involu- 

 tion embracing about tvvo-liflhs of the depth of the whorl; umbilicus wide 

 and shallow, with walls not always abrupt; keel reduced, but distinct, gener- 

 ally consisting of an obtuse angle surmounted by a low, thin keel, not 

 serrated; surface ornamented with about forty-eight to iifty-two simple 

 flexuous ribs, usually arising in pairs from the small, rounded, umbilical 

 tubercules, and crossing the sides of the whorl obliquely forward. There 

 are also a few subordinate ribs that do not extend above the middle of the 

 sides. There is a single row of inconspicuous tubercules along the ventral 

 margin of the whorl that forms an angle between the flattened sides and 

 the beveled ventral surface. On the older shells these tubercules become 

 almost obsolete, as they are also upon young shells. Upon approaching 

 these tubercules the ribs bend more obliquely forward, and in tlie old shell 

 appear to cross the ventral surface, forming on the keel a faint crenulation. 

 On coils with a diameter of less than .8 cm. the ribs are not often seen, the 

 shell being almost smooth. The keel first makes its appearance, at a 

 diameter of.3cm.,as a faint line upon the ventral margin of the whorl. 

 The section of the whorl at this diameter is almost circular. The ribbing 

 begins with the development of the tubercules upon the outer margin, 

 which is followed by the extension of the ribs upward, and later, by the 

 appearance of the umbilical row of tubercules and a downward extension of 

 the ribs from them. 



The largest example of this species collected has a diameter of 4.3 cm., 

 though fragments of still larger coils were found which may belong to it. 



S. oregonensis is related to S. propinqiia Stoliczka, 

 though easily separable from it. 



A variety of S. oregonensis, of which a few small speci- 

 mens were collected, has considerably finer ribs, the 



