MO'LLUSCA. 473 



1886. Camptonectes (Amusium) Burlingtonensis Whitf., Pal. 



N. J., vol. I (Monog. U. S. G. S., vol. 9), p. 53, pi. 



8, figs. 3-6, 9 (not 7r8). 

 1905. Pecten helliscidptus Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. II. 



Description. — Shell, in large individuals, attaining a height of 

 35 mm. to 40 mm., and a width of 30 mm. to 36 mm., the height 

 usually considerably greater than the width, but the two dimen- 

 sions nearly equal in some iridividuals ; hinge-line straight, one- 

 half or less than one-half the width of the shell, the beaks situ- 

 ated back of the middle point of the hinge; the body of the shell 

 subovate in outline, the auriculations sharply differentiated, un- 

 equal, the anterior ones being much broader than the posterior; 

 cardinal slopes usually a little concave, diverging from the beaks 

 at an angle of 90° or less. Right valve depressed convex with 

 a rather deep byssal sinus in front; left valve more strongly 

 convex. Surface of both valves, marked by fine, even radiating 

 ribs with much narrower interspaces; by reason O'f their fre- 

 quent bifurcation the ribs maintain essentially the same size 

 throughout and at the sides of the valves they curve strongly 

 upward in the upper portion, crossing the . cardinal slopes and 

 continuing across the auriculations. Besides the radiating ribs 

 the shells are marked by rather close, concentric raised lines 

 which project slightly as they cross the radiating ribs, and which 

 towards the front of the shell sometimes form fine spines. 



Remarks. — A comparison df the New Jersey specimens of 

 Pecten hellisculptus with authentic examples of Pecten argillen^ 

 sis from Mississippi in the collections of the National Museum 

 at Washington, has failed to disclose any characters which can 

 be considered as of specific value. The only character in which 

 examples from the two localities differ in any noticeable degree 

 is in the strength Oif the radiating markings of the shell, the 

 southern specimens perhaps having these markings slightly 

 coarser. In the present report the specimens from the two regions 

 are united in a single species to which the prior name P. argillensis 

 is given. This species, however, is quite distinct from Pecten bur- 

 lingtonensis with which Whitfield united it ; it does not grow so 



