MOLLUSCA. 819 



to side. Umbilicus small, but open in the shell. Venter sharply 

 rotinded. Septa distant, rather deeply concave; arched forward 

 on the margin of the umbilicus and slightly backward on the 

 sides, but strongly arched forward on the venter. Siphon rather 

 large, situated about two^fifths of the entire distance of the length 

 of the septum from the inner border. Aperture as shown by the 

 section of the volution, longer than wide and deeply emarginate 

 on the inner border by the intrusion of the inner volution, giving 

 it a compressed reniform outline. Surface of the shell unknown." 

 (Whitfield.) 



Remarks. — This species is known only from the type speci- 

 mens, which are two incomplete individuals. The species dif- 

 fers from N. dekayi, which occurs at a lower horizon, in the 

 conspicuous lateral compression of the shell, and the larger 

 umbilicus. 



Formation and locality. — Vincentown limesand, Vincentown 

 (Gabb). 



Geographic distribution. — New Jersey. 



Order AMMONOIDEA. 



Sub-Order LEPTOCAMPYLI. 

 Family SILESITIDAB. 



Genus Pachydiscus Zittel. 



Pachydiscus complexus (Hall and Meek)? 



Plate CI., Figs. 3-4. 



1854. Ammonites complexus H. & M., Mem. Am. Acad. Arts 



and Sci., n. ser., vol. 5, p. 394, pi 4, figs- i a-f. 

 1861. Ammonites complexis Gabb, Synop. Moll. Cret. Form., p. 



65 (9). 

 1864. Ammonites complexus Meek, Check List Inv. Foss. N. 



A., Cret. and Jur., p. 24. 

 1868. Ammonites complexm Con., Cook's Geol. N. J., p. 730. 

 1876. Ammonites complexus Meek, Rep. Inv. Cret. and Ter. 



Foss. Up. Mo., p. 447, pi. 24, figs. I a-c. 



