372 SYSTEMATIC PALEONTOLOGY 



Family PECTINID/E. 



Genus PECTEN Mliller. 



Subgenus PECTEN ss. 



Pecten (Pecten) humpheeysii Conrad. 



Plate XCVIII, Figs. 10, 11, 12. 



Pecten HumphrojsH Conrad, 1843, Proc. Nat. Inst., BulL ii, p. 194, pL ii, flg. 2. 

 Vola Humphreysii Conrad, 1863, Proc. Acad. Nat. Sci. Phila, voL xiv, p. .583. 

 Pecten Humphreysii Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 4. 

 VoJa Humphreysii Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, pp. 83-34, pi. iv, 



figs. 6-9. 

 Pecten {Pecten} Hidnphrey.sn Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, 



pt. iv, pp. 730, 731. 



Description. — " Suborbicular, inferior valve convex; superior fiat, 

 and with .about seven remote, narrow, convex ribs, and concentrically 

 wrinkled; towards the apex is a concave depression; ears equal, sides 

 direct and straight; inferior valve with the ribs wide, approximate, 

 plano-convex and longitudinally striated; one of the ears emarginate at 

 the base/' Conrad, 1842. 



The inferior valve has usually seven or eight broad elevated ribs, one 

 with eleven ribs, however, was much less convex, showing probably that 

 the requisite strength having been obtained by an increase in the ribbing, 

 the marked convexity characteristic of the seven ribbed valves was no 

 longer necessary. Fine concentric striae are very characteristic of the 

 upper valve and are simulated by the concentric growth lines of the 

 lower one. 



Length, 110 mm.; width, 125 mm. 



Occurrence. — Calvert Formation. Fair Haven, Lyon's Creek, 

 Chesapeake Beach, Plum Point, Truman's Wharf, Wliite's Landing, 

 Eeed's, Centerville, Burch (Dall), (not abundant). 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



Subgenus AMUSIUM Bolten. 



Pecten (Amusium) mortoni Ravenel. 

 Plate XCIX, Fig. 1. 



Pecten Mortoni Ravenel, 1844, Proc. Acad. Nat. Sci. Phila., vol. ii, p. 96. 

 Pecten Jfortoni Tuomey and Holmes, 185.5, Pleioceae Fossils of South Carolina, 

 p. 37, pi. X, figs. 1, 3. 



