MOLLUSCA. 403 



Remarks. — In New Jersey this species has been recognized 

 only in the Cliffwood clays, all the specimens observed being 

 internal casts. The types of the species have not been se6n, but 

 the Cliffwood specimens have been compared with authentic 

 examples from Snow Hill, North Carolina, in the collection of the 

 Philadelphia Academy of Science, and there can be no doubt as 

 to the identity of the New Jersey specimens with those from the 

 South. This species is associated with the last, and may be dis- 

 tinguished from it by its' larger size, its more nearly subtrian- 

 gular outline, and especially by its more strongly arcuate hinge, 

 the hinge-plate bearing the teeth extending far down along the 

 posterior margin of the shell, and also down the anterior margin 

 but apparently not so far as behind. This strongly arcuate hinge 

 is apparently the most characteristic feature of the shell. 



Formation and locality. — Cliffwood clay, Cliffwood Point 



(185)- 

 Geographic distribution. — New Jersey, North Carolina. 



Trigonarca cuneifortnis Conrad. 

 Plate XXX., Figs. 18-20. 



1869. Trigonarca cuneiformis Con., Am. Jour. Conch., vol. 5, 



p. 98, pi. 9, fiig. I. 

 1886. Trigonarca cuneiformis Whitf., Pal. N. J., vol. i 



(Monog. U. S. G. S., vol. 9), p. 88, pi. 12, figs. 17-18. 

 1905. Trigonarca cuneiformis .Johns., Proc. Acad. Nat. Sci. 



Phil. (1905), p. 9. 



Description. — ^"Shell quite small, not exceeding half an inch in 

 extreme length in any of the examples yet observed. Trape- 

 zoidal in outline and quite ventricose. Hinge but little more 

 than one-half the length of the shell, and the area very narrow. 

 Beaks small, slightly incurved. Anterior end of the shell regu- 

 larly rounded ; posterior end elongate, produced below, the pos- 

 terior margin very oblique, so as to make the postero-basal angle 

 quite acute. Hinge-plate very narrow, marked by oblique trans- 

 verse teeth, the anterior end having 10 or 12 directed inward 

 below, and the posterior a somewhat larger number pointed 



