TERTIARF FOSSILS. 25 



Figure, natural size. 



Localiiy and position : From the Pliocene on Mark West Creek, a branch of 

 Russian River, Sonoma County; discovered by Mr. V. S. Staley, after whom it 

 is named. 



This shell can be at once distinguished from D. ponderosa, which is quite com- 

 mon in the Tertiary of California, by its less circular outline, the beaks being 

 placed more in advance, by its being more convex, by its less strongly marked 

 lunule, a differently shaped hinge, and its smooth surface. 



D. Conradi, n. S. 



PI. 5, Fig. 43. 



(Z>. alta, Con.; Proc. Philada. Academy Nat. Sci., 1856, p. 315; not D. alia, 

 Dkr. ; nor D. alta, Con. ; P. R. R. Rep., V. 5, p. 320, pi. 2, f. 2: D. alta, Con.; 

 P. R. R. Rep., Vol. 6, p. 71, pi. 3, fig. 13, 13 a.) 



Shell rather small, thin, very elongated; heaks prominent, 

 margins rounded. Lunule deep. Surface marked by concentric 

 lines of growth. 



Figure, natural size. 



Localities: San Emidio Ranch, near Fort Tejon; also "Monterey" (Dr. New- 

 berry). From the Miocene. 



The original of Mr. Conrad's figure having been a distorted specimen, I have 

 prepared the present drawing for the purpose of showing the true outline of the 

 species. Unfortunately his name was preoccupied, and I have therefore dedi- 

 cated the species to the pioneer of Tertiary Palaeontology, not only for California 

 but of the Atlantic States as well. 



TAPES, Megerle. 



? T. TRUNCATA, n. S. 

 • PI. 7, Fig. 44. 



Shell large, thin, transverse; heaks in advance of the middle, 

 pointed forwards ; anterior and posterior ends nearly equal, 

 rounded ; base broadly and regularly convex. Surface marked 

 by numerous small, radiating ribs, nearly obsolete posteriorly. 



PAL. VOL. II. — 5 



