LAMELLIBRANCHIATA OF THE PLASTIC CLAYS. 25 



for such. They also seem to be alHed in general form to Homomyaj Ag., and 

 to some of the smooth forms of Plioladomya^ but in the lunule and the thick- 

 ened shell, are different. Very little is really known of the hinge characters, 

 but on some of the best casts the imprint of a strong tooth on the left 

 valve in front of the line of the beaks shows relations to Veniella, I am 

 in hopes to obtain better material for illustrating the genus before the com- 

 pletion of this work. 



Ambonicardia Cookii, n. sp. 

 Platell, Figs. 11-14. 



Shell large and ponderous, with heavy, massive, incurved beaks, which 

 are strongly enrolled and situated near the anterior end of the shell. Valves 

 very gibbous, very inequilateral and transverse, strongly cuneate in a 

 cardinal view when united, being extremely ventricose opposite the beaks 

 and gradually but rapidly decreasing in depth toward the posterior end; 

 obliquely ovate in outline, with a short, obtusely pointed anterior end, 

 straight but short cardinal line; prolonged but obtusely rounded posterior 

 end; basal line strongly curved, rapidly declining from the anterior end, 

 and distinctly sinuate near the middle of the shell by a broad, shallow, but 

 well-defined oblique sulcus, which passes from the beak to the basal margin 

 just in front of the strongly rounded and prominent umbonal ridge. Ex- 

 ternal ligament strongly marked, and extending the length of the posterior 

 cardinal line and deeply imbedded in a narrow escutcheon. Lunule large 

 and deep, strongly defined, with sharply angular margins. Substance of 

 the shell thick and dense, and the surface marked witli close comparatively 

 strong concentric lines or ridges, and apparently with a thick epidermis. 

 Anterior muscular scar large and deep, situated close to the margin in the 

 pointed anterior end Other muscular imprints not determined and the fea- 

 tures of the hinge are as yet unknown. Pallial line apparently simple. 



The general features of this shell remind one of a deep-valved and 

 strong-beaked Unio, but the hinge has certainly been destitute of lateral 

 teeth, and the form and position of the anterior muscular impression is such 

 as at once to preclude all possibility of its reference to that genus. 



Localities. — The species has been obtained from the clays at Sayre and 

 Fisher's banks near Sayreville, N. J., and at clay banks of R. N. and H. 

 Valentine, near Woodbridge, and at East Brunswick, New Jersev. 



