LAMELLIBEANCHIATA OF THE LOWER MARLS. 67 



one he used in his description. The form is extremely ventricose, especially 

 on the anterior half, and narrowing rapidly posteriorly, with the posterior 

 part strongly curved downward as far as preserved. The following is Mr. 

 Gabb's description as copied from the work cited above. "Tube robust, 

 curved short, portion containing the shell broad, grooved at the anterior 

 half of the back, rounded carinate the rest of the length. Opposite face 

 more narrow and deeply grooved. Extremity distinctly trilobate. Shell 

 unknown. From the shape of the tube it appears related to the preceding- 

 species {L. Repleymms), but the beak is less prominent in advance, the shell 

 is nuich more gibbous, the basal margin more emarginate, and the posterior 

 cardinal margin more depressed." The specimen above referred to, which 

 is that figured on the plate, corresponds exactly with his description of its 

 dimensions and in other particulars, but I should consider it a representative 

 of the shell rather than of the tube only. 



Formation and localiUj. — The specimen was from the Lower Gi'een Marls 

 of New Jersey, but the exact locality is not known. Mi*. Gabb thought it 

 probably from Burlington County, and it is the only specimen of the form 

 known. 



Lithodomus Ripleyaua. 

 Plate XVII, Figs. 4 and 5. 



Llthophagus Ripleyana Gabb. Proc. A. N. Sci.,Phil., ISGl, p. 124. Meek, Check-list, 



p. 11. Geol. Snr. N. J., 186S, p. 726. 

 L. affinis GAhh. Proc. A. N. S., Phil., 1876, p. 31L 



Shell small, length probably not exceeding three-fourths of an inch, 

 very ventricose anteriorly when viewed from the dorsal side, but with nearly 

 parallel dorsal and ventral margins as seen in a side view. Beaks anterior 

 or nearly terminal, incurved and somewhat tumid, as seen in the cast, 

 posterior extremity of the shell compressed. Dorsal margin impressed and 

 the ligament extending nearly one-half the length of the shell. Shell 

 structure unknown, the specimens all being internal casts. 



This species is much more slender and less inflated anteriorly, as seen 

 in the internal casts extracted from within the burrows, than L. affinis. I'he 

 posterior end seems to have been commonly prolonged and curved down- 

 ward very decidedly near the extremity, and also to have been sharply 



