384 CRETACEOUS PALEONTOLOGY. 



Description. The dimensions of one of the type specimens 

 are: length, 15.5 mm.; height, 9 mm.; convexity, 2 mm. Shell 

 subelliptical in outline, the valves depressed convex, somewhat 

 compressed in front and behind. Beaks scarcely elevated above 

 the hinge-line, situated about two-fifths the length of the shell 

 from the anterior extremity. Both the anterior and posterior por- 

 tions of the hinge-line straight or nearly straight, the posterior 

 portion with 20 or more teeth, the anterior portion declining 

 from the beak at an angle of about 46 with the posterior portion, 

 with about 15 teeth. Anterior margin of the shell rounding from 

 the anterior extremity of the hinge-line, the greatest extension at 

 about the mid-height of the shell ; posterior margin rounding from 

 the posterior extremity of the hinge-line, the greatest extension 

 above the middle ; ventral margin, between the most anterior 

 and posterior points of the shell, approaching a longitudinal 

 semiellipse, but with the posterior portion more or less obscurely 

 obliquely subtruncate. Surface of the shell smooth, as indicated 

 by impressions of the exterior. 



Remarks. This species resembles Y. longifrons of the Wood- 

 bury clay, but is proportionately shorter with the basal margin 

 more strongly curved and the anterior and posterior portions of 

 the hinge-line forming less nearly a straight line ; it has not been 

 observed to grow as large as the larger individuals of Y. longi- 

 frons from Lorillard. The species also resembles Y. evansi M. & 

 H., from the Cretaceous beds of the interior, but it differs from 

 that species as illustrated by Meek 1 in much the same way that 

 it differs from Y. longifrons, Y. longifrons and Y. evansi prob- 

 ably being more closely allied than Y. cliff zuoodensis and Y. 

 evansi. 



Formation and locality. Cliffwood clay, Cliffwood Point 

 (105, 185), near Matawan (107). 



Geographic distribution. New Jersey. 



. Inv. Cret. and Ter. Foss. Up. Mo., p. in, pi. 28, figs. 10 a-c- 



