GASTEROPODA OF THE LOWER GREEN MARLS. 169 
DENTALIUM (FALCULA) FALCATUM. 
Plate xx, Figs. 12-18. 
Dentalium faleatum Conrad: Am. Jour. Conch., vol. 5, p. 44, Pl. m1, Figs. 12, 16. 
Dentalium (?) 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. 188, Pl. 
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 stri, 
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 Green 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 Mollusca of the New Jersey formations, I am 
not to be supposed as considering it moliuscan 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. 
