EOCENE PECTENS. 53 



ears orniimented by nmncrdiis, sharp, imbricating laiupUiv of orowth. which appear 

 more in'ominently on tiie anterior portion of the disk; posterior ear short, slightly 

 obliquely truncated, atid sculptured by numerous radials and imliricating lamella; 

 anterior ear unknown. l)ut probalily much longer than posterior. 



Dimenslona. — Alt. ?>>< mm.: long. 30 mm.: hinge line (restored and ajjproximate) 

 18 mm. : diameter 7 nun. 



This species is closely allied to /'. traski Gabb, from the ('retaceous of the 

 Pacific coast. It differs from the latter, however, in not having the diagonal 

 microscropic sculpture so characteristic of that species. 



A fragment of a much larger specimen than the type of 1'. pmaivix, from the 

 same beds and probably the same species, shows, near the periphery, narrow 

 ridge- like ribs separated l)y rather wide interspaces in each of which are two or 

 three fine thread-like riblets. (PI. II, fig. 8.) 



The type of P. j>ri/ar)is, which is now in the collection of the department 

 of geology, Stanford University, is a poorly preserved cast of a left valve 

 on which part of the original shell matter is still preserved. It came from 

 beds of probable lower Eocene (Martinez) age in the ridge between the 

 headwaters of Pescadero Creek and San Lorenzo River, San Mateo County. 

 At this locality it was associated with the following fauna: Terehrat ulhui tejonewiln, 

 Trlton'mm (cf.) (■aliforiiicion. Patella (cf.) fm>ikl, IRicion di.chotoma, (htrea (aff.) 

 idriae/isis, Turho sp.. Aaiata or Patella sp., Tei-ebratxda n. sp., Vidarh (?) spines 

 Semele sp. After an e.xamination of the above fauna Doctor Stanton was of the 

 opinion that it was younger than the Chico (Cretaceous). It is certainly not 

 typical Tejon (middle or upper Eocene), but appears to be closer to the Martinez 

 fauna than to ■a\\\ other, and is, therefore, tentatively placed in the horizon of the 

 latter. 



RANGE. 



Lower Eocene (Martinez 0- Between the headwaters of Pescadero Creek and the 

 San Lorenzo River. San Mateo Coimty (H. S. Gay; Arnold). 



PeCTEN (pROPEAMUSIUM) INTERRADIATUS GaBU. 



PI. II, figs. 9, 10, and 11. 



1869. Pecten iidermdiaiuf: tiabli, Pal. Cal., vol. 2, 1869, pp. 199-2(10, pi. 3S, fi^s. 9S, 98a. 

 1888. Pccteii intermcUatus Uabb, Cooper, Seventh Ann. Rept. Cal. St. Min., ISST, p. 289. (From 

 "Cretaceons B," which is B^orene). 



Description .^^^' i'lheW small, subcircular, ecpiivalve, equilateral, compressed, thin; 

 upper [left] vah'e, ears equal, moderately large: lower [right] valve, right ear long, 

 deeply and narrowly emarginate. Surface marked by very numerous tine radiating 

 lines, and obscure lines of growth. Internal surface of both valves bearing 8 

 straight, equidistant, large ribs of variable length among themselves, extending 

 from the beaks to near the middle of the shell and ending abruptly." 



Dimensians. — Alt. 25 mm.; long. 24 mm.; hinge line 15mm.; diameter 2.5 mm. 



This species may be distinguished from P. sta/iforde»s/'s by its larger size, 

 narrower anterior ear of right valve, and fewer number of interior ribs. It is also 

 distinguishable from P. dallamensis and P. waylandi by its larger size and incon- 

 spicuous external surface sculpture. 



