MARYLAND GEOLOGICAL SURVEY 727 



The genus has been reported from deposits as early as the Carboniferous. 

 The customary habitat of the present day species is in burrows excavated 

 in the floating timber and driftwood of the warm and temperate seas. 



MARTESIA CRETACEA Gabb 



Pholas cretacea Gabb, 1860, Jour. Acad. Nat. Sci., Phila., 2d ser., vol. iv, p. 



393, pi. Ixviii, fig. 18. 

 Pholas cretacea Meek, 1864, Check List Inv. Fossils, N. A., Cret. and Jur., 



p. 16. 



Pholas ? cretacea Conrad, 1868, Cook's Geol. of New Jersey, p. 728. 

 Martesia cretacea Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 304. 

 Martesia (Pholas) cretacea Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, 



p. 190, pi. xxv, figs. 20-23. 



Pholas cretacea Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 18. 

 Martesia cretacea Johnson, 1905, Ibidem, p. 18. 

 Martesia cretacea Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, p. 



654, pi. Ixxiv, figs. 8-11. 



Description. " Tube conical, rounded at the widest end, surface 

 marked by oblique lines ; shell ( ?) ." Gabb, 1860. 



Type Locality. Earitari Bay, Xew Jersey. 



" Shell small, subhemispherical in front, cuneate behind, the beaks 

 strongly incurved, umbones prominent. The anterior margin rounding 

 regularly from the anterior extremity of the hinge line into the straight 

 basal margin, posterior margin subtruncate, post-cardinal margin sloping 

 backward from the posterior extremity of the hinge line. Surface of each 

 valve marked by a deep, narrow groove extending from the beak obliquely 

 backward to the ventral margin which it meets in front of the middle of 

 the shell; in most individuals a second groove close to and parallel with 

 the first, but a little wider and shallower, is introduced a short distance 

 below the beak and continues to the margin. The anterior region of the 

 shell is marked by fine costas which bend abruptly upward in front of the 

 oblique grooves, continuing to above the middle of the shell, where they 

 make a nearly rectangular turn and continue in a horizontal direction to 

 the anterior margin, surrounding two sides of, and sharply differentiating, 

 a smooth, triangular, slightly raised area in the antero-ventral region of 

 each valve. The posterior region of the shell is marked by broader 

 rounded costae, parallel with the margin of the valves. 



