CRETACEOUS FOSSILS. 195 



ritory, east of Paget Sound, were presented by Mr. Samuel Hubbard to tbe Cali- 

 fornia Academy of Natural Sciences. In Colusa County, east of Clear Lake, I 

 found tbis sbell forming almost tbe entire bulk of some beds, interstratified with 

 tbe white limestones. The Mount Diablo specimens are rare, and always small, 

 while some from Colusa and Lake Counties are nearly three inches in greatest 

 length. The only species that I have ever found associated in the same strata 

 with the present one, is Belemnites impressus, which I have found at almost every 

 locality of the Aucella, and which is also very characteristic of the most typical 

 beds of the Shasta Group, in the vicinity of Cottonwood Creek. 



PINNA, Linn. 

 I\ Brewerii, Gabb. 



PI. 32, Fig. 93. 

 (P. Brewerii, Gabb; Pal. Cab, Vol. 1, p. 188, pi. 25, fig. 175.) 



This is a rare species, and I have had the opportunity of ex- 

 amining but few specimens. A very tine one now before me, 

 and for the loan of which I am indebted to the kindness of Mr. 

 Yoy, of Oakland, exhibits the specific characters better than any 

 other yet discovered. The angle of divergence of the sides in 

 this case, is nearer 40° than 20°. Near the middle of each valve 

 is a strongly marked rib, on one side of which are six or seven 

 fine, slightly elevated, radiating ribs; on the other side are two 

 or three similar, obsolete radiations, and starting from the mar- 

 gin are some stronger, but irregular undulations, parallel with 

 the midrib, which run downwards and curve inwards towards the 

 middle ; from the lines of growth, the base of the shell seems to 

 have been notchedan the middle. 



The figure is natural size. Found only in tbe Cbico Group; the present speci- 

 men being from Shasta County. 



