56 TERTIARY AND (JUATERNARY PECTENS OF CALIFORNIA. 



So far as is known, P. Imvmerl is contined to the lowest horizon of the 

 Miocene and top of the Oligocene. It is very abundant at the type locality, 

 Tuff Hill, near Stanford University. One large right valve was also obtained 

 from the fine sandstone immediately overlying the San Lorenzo shale series 

 (Oligocene) in Twobar Creek, near the town of Bouldei- Creek. Santa Cruz 

 County. 



The type, like all of the known specimens of the species, is a njold, and is 

 now in the collection of the department of geology, Leland Stanford Junior 

 Cniversity. Named in honor of Dr. J. C. Branner, professor of geology in that 

 institution. 



RANGE. 



Miocene (lower). Tuif Hill, Stanford University. Santa Clara County (Branner; 



J. P. Smith; Arnold). 

 Oligocene (upper) or Miocen(> (lower). Twobar Creek, near Boulder Creek, Santa 



Cruz County (Newson; Arnold). 



Pecten (Pseudamusium) peckhami (rabb. 



PI. Ill, figs. 6, 7, and 8. 



1869. Perlen peckhami Gabb, Pal. Cal., vol. 2; 1869, pp. .59, 60, pi. 16, figs. 19 and 19a. 

 1888. Peden ptrklinm: Gabb, Cooper, Seventh Ann. Rept. Cal. St. Min., 1888, p. 258. 

 1898. Pecten peckhami Gabb, Dall, Tran.«. Wagner Free Inst. Sci., vol. 3, pt. 4, 1898, \>. 70.5. 



Descriptiim. — Shell averaging about ;i(» millimeters in altitude, subcircular, sub- 

 equivalve, .slightly inequilateral, thin, usually compressed, and with smooth margins. 

 Right valve with the disk showing several small, more or less obsolete, irregular 

 concentric undulations, numerous fine incremental lines and numerous fine obsolete 

 radiating lines; hinge line about two-thirds of the longitude of the disk; anterior 

 ear produced, separated from the body of the shell by a marked groove and a deep, 

 narrow sinus, and prominently sculptured by (> or 7 radiating I'idges and numerous 

 concentric elevated incremental lines; posterior ear not separated by an\' distinct line 

 from the disk surface and ornamented only by concentric lines and obsolete undula- 

 tions. Left valve similai- to right except that the anterior ear is flat, the swell of 

 the shell commencing with nearly a right angle with the ear surface; surface of 

 anterior ear usually sculptured only by incremental lines, but occasionally with 

 radiating stria? also. 



Dimensions. — Alt. 21 mm.; long. i!l mm.; hinge line 14 mm.; diameter 12 mm. 



As a rule only the molds or casts of this species are found in the shales in which 

 they occur, and for this reason some of the characteristics of sculpture of the species 

 are generally lacking. For example, in a large series of specimens examined, onlj' 

 two or three of the shells showed the radiating sculpture. The disks are generally 

 obliquely distorted and often compressed, but the sculpture on the anterior ear of 

 the right valve is almost alwaj's present and is quite characteristic. 



In California this species is found from the San Lorenzo formation (Oligocene) 

 to the Monterey or middle Miocene. P. j}ec7>-h(nnl is found abundantly in the 

 Monterey shale in Newell Creek canyon, 2 miles above Ben Lomond, Santa Ciruz 

 County, where it is associated with Area inontereyana Osmont, Corbula sp., Cyth- 



