362 CRETACEOUS PALEONTOLOGY. 



Description. Shell small, plicated, with the plications of the 

 two valves opposite instead of alternate, the front margin of the 

 shell being 1 produced into tooth-like serrations where the plica- 

 tions terminate ; subpentagonal in outline, attaining a length and 

 breadth of from i mm. to 3 mm., the two dimensions usually 

 being nearly equal ; the greatest width usually along the hinge-line, 

 but sometimes between that line and the front of the shell. Pedi- 

 cle valve strongly convex, with a prominent beak marked by three 

 or four strong, rounded plications upon each lateral slope, and 

 in the larger individuals by an additional mesial plication which 

 originates somewhat abruptly near the mid-length of the shell 

 and continues to the anterior margin; cardinal area sharply 

 defined, triangular, nearly flat or slightly concave, with a strong 

 backward slope, and with a large triangular delthyrium. 

 Brachial valve much flatter than the pedicle, somewhat com- 

 pressed towards the cardinal extremities and with a distinct 

 mesial flattening or sinus-like depression; marked by plications 

 similar to those of the pedicle valve; internally the brachial valve 

 has a strong median septum, the remaining portions of the 

 brachidium not observed. Shell substance strongly punctate, and 

 the surface of each valve marked by one or two somewhat con- 

 spicuous lines of growth. 



Remarks. This little shell is frequently met with in the wash- 

 ings from the Vincentown limesand, near Vincentown, but it is 

 easily overlooked because of its small size. With the exception 

 of the imperfectly known C. plicatilis, which is associated with it, 

 this is the only known American species of the genus Cistella. 



Formation and locality. Vincentown limesand, Vincentowrr 



(154). 

 Geographic distribution. New Jersey. 



Cistella plicatilis Clark. 



1895. Cistella plicatilis Clark, Johns Hopkins Univ. Circ., vol. 

 xv., No. 121, p. 3, Plate, fig. D. 



Description. Pedicle valve unknown. Brachial valve attain- 

 ing both a length and width of 4.5 mm. in the type specimen; 

 orbicular in outline, slightly convex, with 10 or 12 plications. 



