662 CRETACEOUS PALEONTOLOGY. 



1905. Dentalium subarcuatum Johns., Proc. Acad. Nat. ScL 



Phil. (1905),?. 18. 

 1905. Dentalium ripleyanum Johns., Proc. Acad. Nat. ScL 



Phil. (1905), p. 1 8. 



Description. Shell small, usually preserved in the form of 

 casts, in which condition it is circular in cross section, gradually 

 tapering, slender, and gently arcuate; a large individual 47 mm. 

 in length has a maximum diameter of 5 mm., and a minimum 

 diameter of 2 mm. Surface of the casts smooth or with faint, 

 longitudinal ridges; when perfectly preserved they are marked 

 along the median line of the dorsal or concave side by a slightly 

 elevated, rounded ridge with a flattened area on each side, and 

 upon the ventral side by a pair of depressed lines. Surface of 

 the shell marked externally, as shown by impressions of the out- 

 side, by about 12 angular, longitudinal ribs, and by fine annular 

 striae. 



Remarks. In the recent collections this species has been seen 

 most commonly in the Woodbury clay at Lorillard, where it 

 occurs in the condition of internal casts with the external im- 

 pressions of the shell preserved in the matrix. These specimens 

 are certainly identical specifically with the example having the 

 shell partially preserved which has been figured by Whitfield. 

 The type of the species is an internal cast, apparently from the 

 Merchantville clay-marl, whieh shows faint indications of the 

 external longitudinal ribs. The Woodbury clay specimens agree 

 with the type in curvature and in dimensions, and their identi- 

 fication with D. subarcwat is doubtless correct, since the same 

 form is certainly known to be present in the Merchantville faunas. 

 The example described by Gabb from Alabama as D. ripleyana 

 seems not to be specifically distinct from the New Jersey shells. 



Formation, and locality. Merchantville clay-marl, near Mata- 

 wan (101), near Jamesburg (141), Lenola (163)-, Merchant- 

 ville (162); Woodbury clay, Lorillard (102), near Matawan 

 (103), Crosswicks (168), near Haddonfield (183). 



Geographic distribution. New Jersey, Alabama. 



