98 PALEONTOLOGY OF NEW JEESEY. 



marl at the base of the Lower Green Marls at Marlborough, Monmouth 

 County, and from the same horizon near Holmdel ; the former from Mr. 

 Schanck's collection and the latter from the Rev. M. Riley. Casts of the 

 L antrosa have been recognized at very many localities of the Lower Marl 

 Beds, among which Holmdel, Freehold, and Monmouth are the most prom- 

 inent. One specimen of a cast from Freehold is very large, and must have 

 measured quite three and a half inches transverse diameter when entire. 

 The largest specimen from the nodules of white sand, which retains the 

 shell in part, would measure, if restored, fully two and three-fourths inches. 



Idonearca vulgaris. 

 Plate XIIl, Figs. 1-5. 



Cucullcea vulgaris Morton. Synopsis, p. 64, PI. Ill, Fig. 8, and PI. XIII, Fig. 5. Gabb, 



SyDop., p. 118. Meek, Checklist, p. 8. 

 Idonearca vulgaris (Conrad). Meek, Geol. Surv. N. J., 1868, p. 725. Gabb, P. A. N. 



Sci., Phil., 1876, p. 313. 

 Cucullcea terminalis Conrad. Mex. Boundary Surv., p. 148, PI. lY, Fig. 2. 



The casts of this species are often large and indicate a rather ponder- 

 ous shell, which often attained a considerable size, was trapezoidal in form, 

 very ventricose, and very oblique. The beaks, as shown on the casts, are 

 large, elevated, and distant, with a strongly angular umbonal ridge extend- 

 ing from them backward to the postero-basal angle. The postero-cardinal 

 slope is short and quite abrupt, and the junction of the valves strongly 

 keeled when perfect, though this part is often broken away. The portion 

 representing the line of the cardinal area is curved, and the gash on the 

 postero-cardinal slope formed by the muscular ridge is deep, often wide in 

 old individuals, is situated above the middle of the slope, and extends from 

 the edge of the keel, at this point, to fully two-thirds the distance between 

 the margin and the beaks. Anterior muscular scar often distinctly marked, 

 but faint in many cases. Body of the cast radially striated. 



A cast of a single right valve, which I have referred to this species, 

 preserves the impression of the hinge to some extent, but not sufficiently 

 perfect to show the character of the hinge-line along its middle portion. 

 The valve is less ventricose than many of those where the two are in con- 

 tact. The hinge-line is just two-thirds as long as the length of the shell. 



