374 SYSTEMATIC PALEONTOLOGY 



" Shell small, thin, polished, compressed ; left valve more convex, 

 with about twenty faint, flat, rather irregular obsolete ribs, separated by 

 narrower, shallow sulci, the whole surface with minute Camptonectes 

 striation; right valve with concentric incremental lines and a few faint 

 threads near the beaks and anterior submargin; ears small, subequal; 

 ctenolium present; cardinal and auricular crura developed; interior of 

 left valve faintly fluted, but without lirse. . . . 



"In some of the specimens there are a few feeble concentric undula- 

 tions near the beak of the left valve." Dall, 1898. 



Length, 19 mm.; width, 18 mm. 



Occurrence. — Choptank Formation. Jones Wharf. Calvert For- 

 mation. Plum Point, Charles county near the Patuxent river {fide 

 Cope). (Very rare and quite small.) 



Collections. — Maryland Geological Survey, U. S. National Museum, 

 Philadelphia Academy of Natural Sciences. 



Subgenus CHLAMYS Bolten. 

 Section CHLAMYS ss. 



Pecten (Chlamys) coccymelus Dall. 

 Plate XCIX, Fig. 3. 



Pecten [Chlamys) coccymeluff Dall, 189S, Trans. Wagner Free Inst., vol. ill., pt. iv, 

 p. 741, pi. xxxiv, fig. 1. 



Description. — " Shell small, ovate, inflated, strongly sculptured, with 

 unequal ears; disk with eighteen narrovr, high compressed ribs, with 

 wider interspaces, which near the basal margin carry one or two very 

 small radial threads ; the backs of the ribs support numerous high, evenly 

 spaced, distally guttered, small spines ; in the interspaces only transverse 

 sculpture of wavy incremental lines; submargins small, narrow, with 

 fine, beaded radial threads, which in the left valve also extend over the 

 ears; hinge line short, the cardinal crura developed, sharply cross- 

 striated ; auricular crura present ; interior of the disk fluted in harmony 

 with the external ribs. . . . 



" A single left valve of this elegant species was obtained. From the 

 young of P. Madisonius, which sometimes approach it, it is easily distin- 

 guished by its more oval and inflated form, nearly smooth interspaces, 

 and compressed ribs." Dall, 1898. 



