374 SYSTEMATIC PALEONTOLOGY 



" Shell small, thin, iDolished, 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 Wliarf. Calvert For- 

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

 Cope). (Very rare and quite small.) 



Cdflections. — 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) coccymelum Dall, 189S, Trans. Wagner Free Inst., vol. iii., pt. iv, 

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



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

 unequal ears; disk with eighteen narrow, 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. 



