LAMELLIBRANCHIATA OP THE LOWER MAELS. 99 



and the plate has been wide at the extremities, tlie teeth have been nearly 

 parallel to the outer line, not bent or inclined downward as in I. antrosa. 

 There are four indentations and four ridges on the posterior end, and ap- 

 parently two on the anterior end; but their inner ends are not visible, con- 

 sequently I cannot see if they were recurved at this point. 



There is great variability in the general form, in the degree of obliquity, 

 in the ventricosity of the valves, in the distance between the beaks, and in 

 the abruptness of the posterior-cardinal slope, among the specimens which 

 it seems necessaiy to refer to this species. Much of this is apparently 

 dependent on the age of the shells and on the thickening of the valves, 

 especially along the pallial line. I have not seen any specimens which give 

 the slightest evidence of the sui-face features of the shell, so that of this feat- 

 ure I can say nothing. The species is distinguished from the associated 

 forms principally by its extreme ventricosity and the obliquity of the valves 

 as seen in the casts ; and in most specimens the gash representing the mus- 

 cular ridge is deeper than in the other forms. In the younger individuals 

 the form is proportionally less ventricose, and consequently the beaks are 

 nearer each other and the posterior slope less abz-upt. 



Formation and locality. — Casts of this species are found at very many 

 of the localities of the Lower Green Marls throughout the extent of the 

 formation in the State. There are specimens before me from Holmdel, 

 Freehold, Woodbury, Burlington, Mullica Hill, and Marshallville, New Jer- 

 sey. The species is also recognized from Prairie Bluff, Ala., and it is cited 

 by Mr. Gabb and Mr. Meek from the State of Delaware. 



Genus AXINEA Poli. 



A2inea Mortoni. 



Plate XI, Figs. 23-25. ' 



Axinea Mortoni, Con. Am. Jour. Conch., Vol. V, p. 44, PI. I, fig, 14. 



A. liamula and A. amtralis (Mort.) Gabb. Synop., p. 103, Proc. A. K S., 1876, Vol. 



II, p. 317, Meek, Check-list, p. 8. 

 A. rotunda and A. subaustralis Meek. Geol. Surv. N. J., 1868, p. 725. 



A. subaifstralis D'Orb. Prod, de Pal., p. 243, No. 667. 



Among the shells of Axinea obtained from the cretaceous beds of New 

 Jersey are two distinct species, one of which is nearly circular in outline. 



