Geol.— Vol. II.] ANDERSON— CRETACEOUS DEPOSITS. 97 



perfect state of preservation though broken so that it can 

 be taken apart, revealing the inner coils. 



The shell is discoidal and somewhat compressed when small, but increases 

 in thickness very rapidly with growth; width of full grown whorl somewhat 

 less than the depth; ratio of diameter to width of umbilicus, 3.3:1; walls of 

 umbilicus rounded and sloping; section of whorl oval, sloping on the sides 

 toward the periphery; surface ornamented by transverse, rounded ridges 

 with the customary flexure, bending sharply backward within the umbilicus, 

 and forward in crossing the ventral surface. On the younger coils about ten 

 or eleven grooves are to be seen extending parallel to the lines of growth, 

 and are plainest upon the ventral surface. The involution covers nearly 

 two-thirds of the inner coils. The distinguishing features of this species are: 

 (i) the oval section of the whorl; (2) the rapidly increasing thickness of the 

 sliell after attaining a diameter of three or four inches; (3) the absence ot 

 constrictions which appear on most of the species of this group; and (4) 

 sutural characters. The suture of this species resembles in most points that 

 of Desmoceras hoffmaimi, yet there is at least a specific difference which 

 only a comparison will make clear. These dififerences are to be seen in the 

 siphonal saddle, the divisions of the lateral lobes, and in the regularity of the 

 small digitations on the lobes. There is less uniformity in the forward 

 terminal limits of the saddles than appears in the figures. 



Occurrence. — This species evidently belongs to the 

 Horsetown horizon. It was obtained from the Peterson 

 ranch, in the vicinity of Sites, Colusa County, Cahfornia, a 

 locality not yet very well known, and was found associated 

 with Lytoceras batesi and other Horsetown species. 



41. Desmoceras dilleri, sp. nov. 



Plate IV, Figs. 116-117; Plate X, Fig. 192. 



Shell discoidal, but not compressed; umbilicus wide and shallow, walls 

 rounded but abrupt, broadly rounded on ventral surface; ratio of greater 

 diameter to width of umbilicus 2.5:1; width of whorls equal to depth; invo- 

 lution a little less than one-half, that is covering less than one-half of the 

 inner coils; surface marked by slightly flexuous lines of growth and about 

 six shallow, transverse grooves which bend but little forward in crossing the 

 ventral surface; sides of whorl slope somewhat rapidly toward the periphery. 

 Suture line not minutely divided; both lobes and saddles rather broad; lobes 

 not equally tripartite, saddles bifid. 



Occurrence. — Specimens of this species were obtained 

 from near the mouth of Hulen Creek, Shasta County, 

 Cahfornia. It belongs, therefore, in the upper part of the 

 Horsetown horizon. 



The type is in the collections of the University of 

 California. 



