DESCRIPTIONS OV StTBGENERA AND SPECIES. 51 



EO< 'EXE PECllCys. 



[Those known first to appear in tlie ?:o(;t*iw formal ions.] 



PeCTEN (CllLAMYS) CAI.KINSl n. sj). 



PI. II, figi^. 1 anil 2. 



Driscriptio/i. — Shell averagino- about 85 iiiiiiiiiieter.s in altitude, sulxdrciilar, 

 equivalve or nearly so, e<|uilateral, rather thin, somewhat \ entrieose. and with only 

 .slightly serrate margins. Right valve with the exterior surface ornaniented by 

 about 55 small, .squarish, slightly imbricated ribs, which show a tendency to become 

 dichotomous near the end in .some specimens; interspaces channeled ami about 

 one-half as wide as the ribs; hinge line about three-tifths the length of the disk; 

 ears equal in length, flat and with the swell of the disk commencing at right 

 angles to them; anterior ear sculptui'ed l)y 4 or 5 iinbric:it(>d radiating ridges; 

 byssal notch distinct; posterior ear sculptured in a similar manner to the anterior. 

 Left valve similar to the right except that in the formei- the ribs arc slightly 

 more rounded and the anterior ear has no notch. 



Dhih'nsi(»tx. — Alt. 30 mm.; long. 31 mm.; hinge line IS nun.: diameter tl mm. 



So far as known this species has no closely allied forms in any of lh(> other 

 California Tertiaiy formations, and for that reason is admirtible as a diagnostic 

 form for the Tejon. The type and several othei' specimtMis of this species were 

 among some matei'ial collected by I)i-. H. W. Fairbanks on the north side of the 

 Sisar Valley, north of the Astartt> oil wells. \'entura County. At this locality it 

 was as.sociated with the following characteristic Tejon tauiui: Area sp.. ('urdiuni 

 hreioeri^ Merdri.r Imnii. 2Liiii(ih(s onudiix, Tajii's sp., Tui'rili'Jhi iiPdKiuin, \iiii'ri- 

 airdla plmiicoda Lam. \'ar. Itornii. 



The types of /'. ci/Jk/'/ix/' are now in the <-ollectioii of the Uiii\('rsity tjf 

 California. Named in honor of Mr. Fi-ank C. C-alkins, of the United States 

 Geological Survey. 



R.\XGE. 



Eocene (Tejon). Sisar Valley, ViMitura County (Faii'banks). 



Pecten (Chlamys) laxdksi n. sp. 



PI. ir. tijit^. 3, 4, anil .i. 



[)('Kcripti(>n. — Shell averaging about 31 millimetei's in altitude, about as long- 

 as high, subcircular. inequivalve, equilateral, thin, slightly ventricose. and with 

 serrate raargin.s. Right valve more ventricose than left, and flattening toward 

 the periphery in the adult; surface ornaniented by from ii5 to 40 sul>equal, 

 rounded, more or less imbricate ribs, separated from each other by snbeqnal, 

 concave-liottomed interspaces, which average about as wide as the ribs; hinge line 

 slightly longer than one-half length of disk; ears somewhat unequal, the anterior 

 being slighth' the longer; anterior ear sculptured by 1 prominent radials. while 

 the posterior has from ti to S less prominent ones; byssal notch deep; whole 

 surface of disk and ears crossed bv numerous tine imbricating lamelhe. Left 



