Geol .— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. II9 



Occurrence. — The species is an associate of the preceding 

 one, S. gabbi, and belongs to the Upper Chico of Pence's 

 ranch, Butte Count}^ California. 



The type is in the collections of the University of 

 California. 



65. Schloenbachia siskiyouensis, sp. nov. 

 Plate I, Figs. 19-20. 



Shell discoidal and compressed; umbilicus of young coils about one- 

 third the whole diameter, becoming relatively narrower v\ith increasing age; 

 keel at first simple, but at a diameter of i cm. begins to break up into nodes, 

 which at 3 cm. become entirely separated by moderately wide intervals. On 

 the older shells the segments of the keel form high and narrow tubercules 

 which have a definite and regular position with reference to the ribs. The 

 ribs are simple, about twenty-five in number, and are of two orders. The 

 first originate in the prominent tubercules along the umbilical margin of the 

 whorl, and, bifurcating from that point, terminate in the outer row of 

 tubercles along the ventral margin. The ribs of the second order make their 

 appearance between the pairs of the first. Thus, about every third rib 

 arises from a little above the middle of the side, without extending to the 

 umbilicus, and terminates as do the others, in the external row of tubercules. 

 This outer row of tubercules forms a series of distinct and pointed prom- 

 inences that diverge slightly from the plane of the keel. A little abo\e these, 

 upon each rib, is developed a distinct prominence which forms the thickest 

 portion of the rib, and which is separated from the outer, or marginal node, 

 by a shallow though visible depression. The ribs are inclined to be straight, 

 except where on approaching the outer margin they curve slightly forward. 

 The tubercules of the keel stand a little forward of the marginal nodes in a 

 position to meet exactly the forward curving of the ribs. 



This, together with the following species, appears to be 

 referable to the genus Barroisiceras Gross. It seems to 

 have no close ally either in the deposits of Southern India 

 or in the Interior Basin of the United States. 



66. Schloenbachia knighteni, sp. nov. 



Plate I, Figs. 1-4; Plate II, Figs. 39-40. 



Shell discoidal, compressed; sides flattened in young adult smaller coils, 

 but becoming more inflated in old age, attaining a diameter of 10 cm. ; surface 

 characterized by the possession of about thirty simple and almost straight ribs, 

 most of which originate at the umbilical margin of tlie whorl; one-third of the 

 whole number beginning there in prominent tubercules, the others arising 



