CRETACEOUS FOSSILS. 129 



end unknown, the terminal portion being very much broken in 

 the only specimen I have seen. From the median line, the posi- 

 tion of the mid-rib in most of these shells, the wrinkles diverge 

 backwards and outwards at an angle of about 25°, curving more 

 outwardly as they approach the margin ; these wrinkles are acute 

 on the dorsal face of the shell, and inclose concave interspaces of 

 very variable length ; the longest lines, which originate at the 

 anterior end of the shell, reach the margins about midway be- 

 tween the two extremities. 



Length, 3 inches -f- ; width, 1.2 inches in the middle ; the total length seems to 

 have been from 3.3 to 3.5 inches. Thickness apparently not more than .01 inch, 

 as exposed by several fractures. 



Locality: Shasta Group,* Cottonwood Creek, Shasta County. A single speci- 

 men in my cabinet, found by Mr. Mathewson. 



Belemnites impressus, Gabb 



This is the only cretaceous Bclemnite so far discovered in California. It is one 

 of the most characteristic fossils of the Shasta Group, and besides the localities 

 mentioned in the report of the Survey, Vol. 1, it has been found at various places 

 on the east side of the Northern Coast Eange, more especially in Colusa County, 

 and elsewhere east of Clear Lake. 



* For reasons which will be detailed in their proper place, I consider the group, 

 for which I here propose this name, to be the equivalent, or at least the nearest 

 representative, of the Neocomien. It has been heretofore included, for want of 

 positive grounds of separation, as a provisional member of the " Division A," of 

 the California Cretaceous. I shall, further, in this paper, use the term Martinez 

 Group, for tbe upper portion of "Division A" of the California Reports; the Chico 

 Group, for those beds of which Chico Creek, Pence's Ranch, and Tuscan Springs 

 are typical localities ; and shall call " Division B" theTejon Group, these localities 

 being the points where the respective formations are most strongly developed. 



PAL. VOL. II. — 18 



