aASTEiiOPODA OF tbb lower green marls. 169 



Dentalitjm (Falcula) falcatum. 



Plate XX, Figs. 13-18. 



Dentalium falcatum Conrad: Am. Jour. Conch., vol. 5, p. 44, PI. ii, Pigs. 13, 16. 

 Dentalium (f) hamatus Conrad: Am. Jour. Conch., vol. 6, p. 77. 

 Falcula hamatus Conrad : Am. Jour. Conch., vol. 6, p. 77. 



Not Dentalium hamatum Forbes : Trans. Geol. Soc, London, vol. 7, p. 138, PI. 

 XV, Fig. 8. 



The casts on which this species was founded are small, cylindrical, 

 gradually tapering and strongly curved, with a decreasing curvature as they 

 increase in size, the smaller extremity being very much more curved than 

 the larger parts, where in age they become nearly straight. No indications 

 of a slit, lobation, or ridges mark the casts in any part of their length. A 

 partially exfoliated specimen, preserving a single layer of the shell sub- 

 stance over a part of its extent, shows simply very fine transverse striae, 

 with an indication of a polished interior surface during the life of the 

 animal. 



This very peculiar species presents all the ordinary features of a Den- 

 talium as far as the casts of the interior could preserve them, except in its 

 great and unequal curvature, which is gradually decreasing in extent from 

 the apex to the outer end. In the extent of curvature and in the rate of 

 increase in diameter the different specimens vary considerably. 



Formation and locality : In the Lower Grreen Marls, at Crosswicks, New 

 Jersey. Other fragments occur associated with fragments of Teredo tubes, 

 but without locality marked on them, which may be from other places. 

 Collection Acad. Nat. Sci., Phila. 



Genus Diploconcha Conrad.' 



Geol. North Carolina, vol. 1, 1875, W. C. Kerr. Appendix by T. A. Conrad, p. 12. 



Mr. Conrad bases this genus on a shell from the Cretaceous formation 

 of North Carolina, which he describes as follows: "Shell composed of two 

 adhering tubes, one resting in a furrow on the side of the opposite tube." 



' In placing this genus and species here among the Mollnsca of the New Jersey formations, I am 

 not to be supposed as considering it molluscau in nature. Mr. Conrad described it as a mollusk, how- 

 ever, and the name will be sought there by others, should more specimens be discovered. 



