MARYLAND GEOLOGICAL SURVEY 373 



Pecten Mortoni Emmons, 1858, Kept. N. Car. GeoL Survey, p. 281. 

 Amnsium Mortoni Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. .582. 

 Amusmm Jfortoni Meek, 1864, Miocene Check List, Smith. Misc Coll. (183), p. 4. 

 Fecten (Amusiwn) 3Iortoni Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, 

 p. 757. 



Description. — " Orbicular, thin, both valves moderately convex, one 

 more so than the other — outside, with numerous concentric obsolete 

 strias; inside, — with from eighteen to twenty-four radiating double ribs, 

 slightly elevated; ears large, subequal, striated externally." Ravenel, 

 1844. 



This large, thin, flattened species is rarely obtained entire, it is quite 

 rare in Maryland, the Survey having no specimens. A few broken pieces 

 in the National Museum are labelled " Fairhaven and Cove Point." 

 These specimens are probably from Cove Point and the reference to 

 Fairhaven a mistake, since the two localities are separated geographically 

 by about thirty miles and stratigraphically by about almost the entire 

 Maryland Miocene column, rendering it unlikely that through accidental 

 admixture part of the material came from one place and part from the 

 other. The character of the shell substance in the specimens is sound 

 and not unlike that found at Cove Point; while in the Fairhaven cliffs 

 all the shells have entirely lost their shell substance through decay and 

 exist only as casts, except Ustrea percrassa, in which the shell substance 

 is still present but very badly decayed, and Discinisca lugubris which is 

 here as everywhere else still fresh and polished. 



Length, — the fragments indicate a length of about 160 mm. 



Occurrence. — St. Mary's Formation. Cove Point. 



Collection. — TJ. S. National Museum. 



Subgenus PSEUDAMUSIUM H. and A. Adams. 



Pecten (Pseudamusium) cerinus Conrad. 

 Plate XCIX, Fig. 2. 



Fecten cerinus Conrad, 1869, Amer. Jour. Conch., vol. v, p. o9, pi. ii, tig. 2. 

 Fecten {Fseudamusium) cerinus Dall, 189S, Trans. Wagner Free Inst. Sci., vol. iii, 

 pt. IV, p. 758. 



Description. — " Subovate, extremely thin, compressed ; ears equal ; 

 right valve radiately ribbed; ribs very slightly raised and rounded; 

 surface ornamented by minute, close divaricating lines, left valve without 

 ribs." Conrad, 1869. 



