MOLLUSCA. 505 



Modiola burlingtonensis Whitfield. 

 Plate LV., Pigs. 18-19. 



1886. Modiola Burlingtonensis Whitf., .Pal. N. J., vol. i 

 (Monog. U. S. G. S., vol. 9), p. 65, pi. 17, figs. 8-9. 



1905. Modiolus burlingtonensis John., Proc. Acad. Nat. Sci. 

 Phil. (1905), p. 12. 



Description. — "Shell of moderately large size, very ventricose, 

 and w?ith subparallel dorsal and ventral margins, large prominent 

 umbones and incurved beaks situated near the anterior end but 

 not terminal, the anterior margin perceptibly extending beyond 

 them and rounded. Umbonal ridge prominent and subangular, 

 especially near the beaks, and becoming broader and more 

 rounded posteriorly; surface of the valves strongly constricted 

 and sinuate in front of the ridge and the anterior surface again 

 inflated ; cardinal slope comparatively broad and slightly concave 

 toward the postero-cardinal border. Hinge-line straight and 

 three-fifths as long as the shell, and rather strongly impressed in 

 the internal cast; posterorcardinal margin rounding rapidly for- 

 ward from the more narrowly rounded posterior extremity. 

 Surface of the cast, the only condition under which it is known, 

 apparently smooth or marked only by irregular concentric lines 

 of growth, some of which produce undulations of considerable 

 strength on the casts. On one individual there appears on the 

 posterior cardinal slope very faint indications of rather coarse 

 radiating lines, but too faint to warrant the statement that such 

 markings really existed on the shell." (Whitfield.) 



Remarks. — The horizon of this species is not satisfactorily 

 known, as it has not been met with in any of the recent collec- 

 tions of the Survey, and the recorded locality. "Burlington 

 County," is too indefinite to be of much assistance in forming 

 an opinion. The lithologic character of the specimen, however, 

 more closely resembles that of specimens from the Merchantville 

 clay-marl than any others, and it is probable that it was collected 

 from that formation. 



Formation and locality. — Merchantville clay-marl, Burlington 

 County (Whitfield). 



Geographic distribution. — New Jersey. 



