LAMELLIBRANCHIATA OF THE LOWEE MARLS. 123 



Formation and locality. — The specimen is in the collection of the Acad- 

 emy of Natural Sciences of Philadelphia, and on the labels accompanying it 

 is simply marked "Cret, N. J.," without more definite locality. 



Genus SCAMBULA Couratl, 1869. 

 (Am. Jour. Couch., Vol, Y, p. 48.) 



Scambula perplana. 



Plate XVIII, Figs. 8-10. 



Scambula perplana Conrad. Am. Jour. Concli., Vol. V, p. 48, PI. IX, Figs. 7 and 8. 



Proc. A. N. Sci., Phil., 1872, p. 51, PI. I, Fig. 2. 

 Crassatella perjdana (Cou. sp.) Stoliczka. Pal. Indica, Vol. Ill, p. 294 and 295. 



Shell small, triangularly ovate, very transverse, with very sharp, pointed, 

 and recurved beaks, situated just within the middle third of the lengtli of 

 the shell and nearest to the anterior end. Valves flat, marked by fine 

 concentric lines of growth and a few (three or four) broad, oblique' undu- 

 lations of the surface which pass from the posterior hinge-line backward to 

 the basal margin. There are also a few obliquely concentric wrinkles on 

 the antero-cardinal margin which extend only a short distance over the disk 

 of the valve. Along the position of the posterior umbonal ridge, the .^uiface 

 strijB are abruptly deflected upward, marking the position of the ridge and 

 defining the posterior slope of the valve. Posterior end of the valve narrow 

 and truncate; anterior end obtusely angular; basal margin regularly and 

 broadly arcuate. Inner margin of the valves crenulate; muscular scar.s 

 small and faintly marked. 



This shell presents all the appearances of a species of Pandora, oi- 

 perhaps Tellidora, except in the hinge, where there are some slight differ- 

 ences. The left valve appears to have two cardinal teeth which are slighth- 

 curved, and are strongly ci'enulate on their inner or contiguous faces, also 

 a long anterior and posterior tooth parallel to the margins. The opposite 

 valve has a single cardinal tooth or ridge (cartilage bearing'?), which would 

 fit between those of the other valve, and a double ridge on the anterior 

 side, forming a socket for the ridge of the left valve, and a single sharp 

 ridge on the margin of the valve behind, which would fit between the ridge 



