LAMELLIBRANCHIATA FROM BASE OF THE UPPER MA.RLS. 207 



Formation and locality. — The type specimens are marked Vincentown, 

 New Jersey, and are from the collection of the Academy of Natural Sci- 

 ences, Philadelphia, Pennsylvania. There are also specimens from the 

 same locality in the collection at Rutgers College. These are from the 

 lower layers of the Upper Marls; but the same form occurs in the yellow 

 sands of the Middle Beds, and similar forms are given in many European 

 works as occurring in the chalks of Europe under the name Grt/phcea vesi- 

 cularis. 



MYTILIDiE. 



Genus MODIOLA Lam. 

 Modiola Johnsoni, u. sp. 

 Plate XXVIII, Figs. 8,9. 



Shell small, measuring, in the only perfect example of a cast seen, but 

 little more than an inch in its extreme length. Form ovate, widest behind 

 the middle, and somewhat narrowed anteriorly, while the posterior end is 

 acutely rounded; beaks large, tumid, nearly anterior, slightly enrolled and 

 approximate. Anterior end narrow, the projection scarcely extending be- 

 yond the beaks. Valves very ventricose, the umbonal ridge very full and 

 rounded. Ligament short, slender, but distinctly marked; a slight con- 

 striction or sulcus marks the basal half of the width of the shell anterior 

 to the middle of its length. Surface of the shell as seen in casts marked 

 by very fine concentric lines parallel to the margin, and also by several 

 varices of growth at irregular intervals. 



This species somewhat approaches 31. Julia Lea's sp., but is not alate 

 posteriorly as is that species, and the posterior end is mucli more narrowly 

 rounded. It also presents much the appearance of the enlarged figures of 

 Lithophagus inflatus herein described, but is less cylindrical, being fuller or 

 more convex on the basal margin and the beaks are not so broad. It also 

 holds a different geological position. 



Formation and locality. — In the Dark Green Marls below the Eocene 

 beds of the Upper Green Marls at Farmingdale, New Jersey. 



