MOLLUSCA. 66 1 



Because of these peculiar characters, Gabb proposed the generic 

 name Polorthus for these tubes, and expressed the belief that they 

 were allied to the gastropod genus Vermetus; later, however, the 

 same author considered the genus Polorthiis to be a very peculiar 

 type of Cephalopod. Both these interpretations of the tubes, 

 however, are certainly erroneous, and there can be no question as 

 to their relationship with the burrowing pelecypods Teredo. 

 They are certainly distinct generically, however, from the casts 

 of tubes with contained bivalve shells in the lower beds, and 

 Gabb's generic name Polorthus may be retained for them. 

 Among the living Teredidae there are forms with septate tubes 

 similar to those of this Cretaceous form; some do not possess 

 calcareous valves, and some burrow in the sand as these seem to 

 have done, instead of in wood or stone. 



Formation and locality. Vincentown limesand, near Hurff- 

 ville (170, 171), Timber Creek and near New Egypt (Whit- 

 field). 



Geographic distribution. New Jersey. 



Class SCAPHOPODA. 

 Family DENTALIIDAE. 



Genus DENTALIUM Linneus. 



Dentalium subarcuatum Conrad. 

 Plate LXXV, Figs. 1-2. 



1853. Dentalium subarcuatum Con., Jour. Acad. Nat. Sci. Phil., 

 2nd sen, vol. 2, p. 276, pi. 24, fig. 13. 



1860. Dentalium Ripleyanum Gabb, Jour. Acad. Nat. Sci. Phil. 



2nd sen, vol. 4, p. 393, pi. 69, fig. 48. 



1861. Dentalium subarcuatum Gabb, Synop. Moll. Cret. Form., 



p. 105 (49). 

 1864. Dentalium subarcuatum Meek, Check List Inv. Foss. N. 



A., Cret. and Jur., p. 17. 



1868. Dentalium subarcuatum Con., Cook's Geol. N. J., p. 728. 

 1892. Dentalium subarcuatum Whitf., Pal. N. J., vol. 2 



(Monog. U. S. G. S., vol. 18), p. 166, pi. 20, figs. 



19-24. 



