TERTIARY FOSSILS. 59 



Y. IMPRESSA, Coll., Sp. 



(Nucula impressa, Con. ; Wilkes's Exped., p. 726, pi. 18, fig. 7.) 



(Yoldia id., Meek; Check List, Miocene.) 



(Y. Cooperii,'G. ; Proc. Cal. Acad., 1865, p. 189.) 



(Id., G. ; Pal. Cal., Vol. 2, p. 31, pi. 9, fig. 54.) 



(Id., Cooper and Carpenter; Enumerations of W. C. Moll.) 



I described this magnificent species from a single recent valve, and numerous 

 fossils in all the deposits down to the Miocene; and in doing so I was supported 

 in my opinion of its being a nondescript by no less authorities than Cooper and 

 Carpenter, who had been working for years in the mollusca of California, and by 

 Hanley, who had just completed a monograph of the family. More recently, while 

 preparing the following table of synonymy, I have been convinced that Conrad's 

 impressa is merely a young of the same species. My reasons are: first, there is 

 nothing incompatible in the form ; second, the sculpture of the surface, so far as 

 figured in the Wilkes's Exped. Report, is the same as that of Cooperii; and third, 

 I have seen an undoubted specimen of my species from the Miocene of Astoria. 



PECTEN, Brug. 



P. Peckhami, 11. s. 



PI. 16, Fig. 19 a. 



Shell small, thin, subcircular, equivalve, or nearly so, slightly 

 inequilateral ; ears nearly equal in size. Upper valve, right ear 

 not separated by any distinct line from the remainder of the 

 surface ; the corresponding ear of the lower valve has the same 

 character; left ear flat, the swell of the shell commencing with 

 nearly a right angle- with its surface ; corresponding ear of lower 

 valves produced, separated from the body of the shell by a marked 

 groove and a deep, narrow sinus. Surface marked by numerous 

 small, irregular, concentric undulations, crossed by obsolete wavy 

 radiating lines, which are most distinct on the ears. 



From the bituminous shales of the Upper Miocene, on the Ojai Ranch, Santa 

 Barbara County, where numerous specimens were collected by Mr. S. F. Peckham. 



