MOLIvUSCA. 415 



1869. Axinea mortoni Con., Am. Jour. Conch., vol. 5, p. 44, pi. 



I, fig. 14. 

 1876. Axincsa subaustralis Gabb, Proc. Acad. Nat. Sci. Phil. 



(1876), p. 317. 

 1886. Axinea Mortoni Whitf., Pal. N. J., vol. i (Monog. U. S. 



G. S'., vol. 9), p. 99, pi. II, figs. 23-25. 

 1886. Axinea aita Whitf., Pal. N. J., vol. i (Monog. U. S. G. 



S., vol. 9), p. loi, pi. II, figs. 26-29. 

 1905. Pectuncultis australis Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 10. 



Description. — Shell subcircular in outline, varying in size from 

 1 5 mm. to 40 mm. in diameter, the convexity of each valve being 

 from one- fourth to three-tenths the diameter; very slightly 

 oblique, the beaks central in position. The internal casts com- 

 pressed about the free margin especially in adult shells, the 

 margin strongly crenulate when well preserved. The beaks 

 strongly elevated and pointed, their lateral slopes meeting in an 

 angle varying several degrees either way from 90° ; the impres- 

 sion of the hinge-plate broad and arcuate, with 9 or 10 strong 

 teeth on each side of the beak, directed at nearly right angles to 

 the inner margin of the hinge-plate, and with several smaller 

 teeth in the middle beneath the beak. Anterior and posterior 

 muscular impressions well defined, especially in the larger speci- 

 mens. The shell substance thick, marked externally with more 

 or less irregular, concentric lines O'f growth, and by regular 

 radiating costae which are more or less interrupted by the con- 

 centric lines upon partially exfoliated individuals. The beaks 

 approximate and the cardinal areas small with divergent furrows. 



Remarks. — This is the common species of Axinea in the New 

 Jersey Cretaceous faunas and includes both forms, A. mortoni 

 and A. alta, recognized by Whitfield. All of Whitfield's speci- 

 mens were from the Navesink marl, and a careful study of the 

 ones he used along with many others in the recent Survey col- 

 lections, shows them all to be one species. The two forms are 

 connected by all intermediate variations, those called A. aita 

 being only the larger individuals. In the Merchantville clay the 



