74 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



than the rili.s; sart'are of ribs and interspaces sculptured by rather coarse 

 radiating- lines and imbricatiuo- incremental lamelhe; anterior ear longer than the 

 posterior, and with 4 prominent, tinelj imbricated radials; byssal notch rather 

 deep; posterior ear rectangularly truncated, and with radial and concentric 

 sculpture. Left valve similar to right, except with slightly wider interspaces. 

 The disk of this variety is generally contracted after reaching an altitude of iO 

 millimeters or more. 



Diiiu'iisidTin. — Alt. -JrO mm.; long. 47 mm.; hinge line about 30 mm.; diameter 

 about 14 nmi. 



This variety is closely allied to the tj'pical /'. crasx/a/rt?/', and probaljly is 

 the ancesti'al form. It is distinguishable from the latter l)y its smaller size 

 when adult, narrower, lower, and more strongly and evenlj' convex-topped ribs, 

 narrower anterior ear on the right valve, and tendency to become more 

 contracted, and consequently more convex when adult or at an altitude of about 

 00 millimeters. J\ var. /i/uji/ffani resembles J\ I'st/'c/lam's in size and shape, and 

 in the earlier stages of growth is almost indistinguishable on account of having 

 but a single line down the middle of the intersi)ace, which reseml>les the inter- 

 calary riblet of P. ('t<1r<'llaniix. After attaining an altitude of about 30 millimeters 

 the two species are easily separated, as at that stage of growth the radial 

 striation becomes appart'nt on the ribs of P. var. Jiaviilfotii, and the radial line 

 in the interspace is supplemented by others, thus ornamenting the interspace 

 with several radial lines rather than with an intercalary riblet, as in P. esfrd- 

 1(1)1 us. The tendency to undulations caused by temporary contractions in the 

 growth of the disk near th(> umbo is often exhibited to a slight degree in some 

 specimens of P. var. htnniltoni. 



This variety is known only from the Mount Hamilton Range, where it is 

 quite common from a few miles south of Mount Hamilton to Mount Diablo, in 

 Contra Costa County. P. vai-. Jtamntoni occurs in the horizon of the Miocene 

 which is so well developed in the vicinitA' of Alum Rock Canyon, Santa Clara 

 Count_v. The type is from this locality, and is now in the U. S. National Museum 

 (No. 164845). kamed in honor of Mr. \\ . R. Hamilton, of Bodie, Cal. 



Miocene (upper). Alum Rock Canyon, Santa Clara ('ounty (Turner; J. P. Smith; 

 Arnold); Mount Hamilton, Santa Clara County (Crawford); Mount Hamilton 

 Range in Alameda County (Yates). 



Pecten (Lyropecten) estrellanus Conrad. 

 PI. XIX, figs. 1 and lo,- PI. XX, figs. 1, 2, and la; PI. XXI, figs. 1, W/, 1/,, 2, 2n, and 2fc. 



1856. FnlHum eslreUanum Conrad, Pac. R. R. Kept., vol. 6, pt. 2, 1856, p. 71, ]>\. 3, fig. 15. 



1856. Pallium eslrdlanum Conrad, Pac. R. R. Rept., vol. 7, pt. 2, 1856, p. 191, \A. 3, figs. 3 and 4. 



1857. Palliuvi estreUanum Conrad, Proc. Acad. Nat. Sci. Phila., vol. 8 for 1856, p. 313. 

 1863. Lyropecten estrellamis Conrad, Proc. Acad. Nat. Sci. Phila., vol. 6 for 1862, p. 291. 

 1863. Li/ropecten roUtformh Conrad, Proc. Acad. Nat. Sci. Phila., vol. 6 for 1862, p. 291. 

 1869. Lb-opeden estratlanun Conrad, Gabb, Pal. Cal., vol. 2, 1869, p. 105. 



