60 TERTIARY AND QUATERNARY PECTENS OF CALIFORNIA. 



19 ])rominent, ,s<juare, flat-topped, medially sulcated rll)s; interspaces channeled and 

 slightly narrower than ribs; whole surface sculptured l)y fine, regular, <'oncentric 

 incremental lines: hinge line less than one-half length ot disk; ears subenual. 

 convex, and ornamented by concentric lines. Left valve flat or slightly concave, 

 ornamented by about 17 prominent, equal, equidistant, narrow, couxex-topped ribs, 

 which are separated by flat-bottomed interspaces nuich wider than the ribs; surface 

 sculptured by numerous flue, regular, wavy, concentric lines; ears concave and 

 sculptural by concentric lines. 



Ijiniemsiiiihs. — Alt. 36 mm.; long. ■10 mm.; hinge line 15 mm.; diameter S mm.; 

 umbonal angle (left valve) 105 \ 



This species belongs to the group of which 1'. diegensis is the living member. 

 P. mrrizoensls, P. stearnKii, and /'. diegensis taken in chronologic order as above 

 may represent a genetic series. The three species are alike in most respects: They 

 nre all plano-convex, have squarish, more or less sulcated or longitudinally ridged 

 ribs, convex ears on the right valve, and rather narrow, rounded ribs and concave 

 ears on the left. 



P. carrkoensis difl^ers from the other two members of the group in the smaller 

 number and less prominence of its ribs and in its relatively much shallower and 

 narrower interspaces. 



The Pecten mentioned by Dall on page 706 of the Transactions of the Wagner 

 Free Institute as coming from the Miocene deposits near San Diego was compared 

 with the type of P. earrizoensis and found to be of tiiis species. 



The type locality of P. carrizoensis is at the head of Garnet Canyon, about 

 12 miles north of the Mexican boundary, in the Carrizo Creek district, San 

 Diego County. The beds in this district contain a fauna diflerent from any of 

 the other known California formations, but from other considerations it is deemed 

 almost certain that the deposits are of Miocene age. Just what horizon the beds 

 represent has not yet been determined. (See list of Carrizo Creek disti'ict fossils 

 in Part I, p. 22, and list of Santa Rosalia, Lower California, fossils under P. eerro- 

 sensis var. iiiendenhalll, p. 85.) 



The tj'pe of P. carrhoetixiK, which was collected by Dr. Stephen Bowers, is 

 now in the collection of Dclos Arnold. 



Miocene. Head of Garnet Canyon, 12 miles north of Mexican boundary, San 

 Diego County (Bowers); Santa Rosalia, Lower California, west of and across 

 the Gulf from Guaymas, Mexico (G. P. Merrill; E. Palmer). 



Pecten (Pecten) krepi n. sp. 



PI. V, fig. 1; PI. VI, figs. 1 ami la. 



Demi'iption . — Shell averaging about 75 millimeters in altitude, longer than 

 high, plano-convex, ecjuilateral, and with smooth margins: sides concave above; 

 lateral area ver}' broad. Right valve ventricose and ornamented by about 20 

 low, broad, rounded ribs, separated by shallow interspaces in which are low, broad 

 intercalaries; the sulcation on the interior of the valve corresponding to the 



