MOLLUSCA. 66 1 



Because of these peculiar characters, Gabb proposed the generic 

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

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

 same author considered the genus Polorthus 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 

 Cabb'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. 



Pormation and locality. — Vincentown limesand, near Hurff- 

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

 field). 



Geographic distribution. — New Jersey. 



Class SCAPHOPODA. 



Family DBNTALIIDAB. 



Genus Dentauum Linneus. 



Dentalium subarcuatum Conrad. 



Plate LXXV., Pigs. 1-2. 



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



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

 i860. D£ntalium Ripleyanum Gabb, Jour. Acad. Nat. Sci. Phil. 



2nd ser., 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. 



