500 NORTH AMERICAN INDEX FOSSILS. 



372. P. argillensis Conrad. (Fig. 672.) Cretacic, 



Right valve depressed-convex ; left valve more convex. Sur- 

 face of both valves marked with fine, even, bifurcating, radiating 



striae and close concentric lines which 

 project slightly as they cross the radii. 



New Jersey (Merchantville-Navesink ;; 

 especially typical of the Woodbury), 

 Mississippi, Texas. 



373. P. stearnsii Dall. (Fig. 675, e.} 



Pliocenic. 

 Right valve with about 26 square ribs 

 separated by narrower interspaces ; top 

 Fig. 672. Pecten argillensis, of each rib marked by a median shallow 



nghyalve.^ (After Whitfield, grooye and by Qne Qr twQ { ^ ^^ 



on each side of the groove. Surface 

 crossed by concentric lamellae finer and twice as crowded on the 

 right valve as on the left. On the left valve the interspaces are 

 wider than the rounded ribs. Differs from P. healeyi in its radial 

 striation and more numerous ribs. 

 California. 



XCVIII. Chlamys Bolton. ' 



A nearly equivalve Pecten, with small, unequal ears (posterior 

 the smaller) and deep byssal notch on whose edge is a well- 

 developed comb-like series of small teeth (ctenolium) in which 

 the byssal threads rested.? Surface of shell marked with radial 

 ribs or striae. Concentric lines often elevated into little tongue- 

 like extensions where they cross the radii. Triassic-Recent. 



374. Pecten (Chlamys) complexicosta Gabb. (Fig. 673, g.) 



Comanchic. 

 Surface marked with minute radiating striae and with 12 to 14 

 obscure radiating ribs with at times smaller ribs intercalated. 

 Very abundant in Knoxville of California. 



375. P. (Chlamys) nebrascensis Meek and Hayden. Cretacic. 

 Small, suborbicular. Hinge line less than length of valve 



below. Both ears separated from body of shell by rather angular 

 depressions. Surface of each valve marked with 12 to 15 large, 

 usually simple, angular, radiating ribs, separated by furrows of 

 about the same width as the ribs. 



