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 O'f the shell rounding from 

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

 about the mid-height of the shell ; poisterior 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^ in much the same way that 

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

 ably being more closely allied than Y. clifFwoodensis and Y. 

 evunsi. 



Formation and locality. — Cliffwood clay, Cliffwood Point 

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



Geographic distribution. — New Jersey. 



'Rep. Inv. Cret. and Ter. Foss. Up. Mo., p. iii, pi. 28, figs. lO a-c- 



