MOLLUSCA. 625 



1861. Siliquaria biplicata Gabb, Synop. Moll. Cret. Form., p. 



226 (170). 

 1864. Siliquaria biplicata. Meek, Check List Inv. Foss. N. A., 



Cret. and Jur., p. 15. 



1867. Leptosolen biplicata Con., Am. Jour. Conch., vol. 3, pp. 



15 and 188. 



1868. Leptosolen biplicata Con., Cook's Geol. N. J., p. 727. 

 1876. Leptosolen biplicata Gabb, Proc. Acad. Nat Sci. Phil. 



(1876), p. 304. 

 1886. Leptosolen biplicata Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 183, pi. 25, figs. 1-2. 

 1905. Leptosolen biplicata Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), P- 17- 



Description. — The dimensions of an average specimen are: 

 length, 35 mm.; height, 11 mm.; convexity, 3 mm. The largest 

 example observed is nearly 60 mm. in length. Shell elongate, 

 with straight, subparallel dorsal and ventral margins, the anterior 

 and posterior margins rounded, the anterioi- usually a little more 

 sharply rounded than the posterior, the greatest anterior exten- 

 sion at or above the mid-height of the shell. Gaping at both ends, 

 more widely so^ posteriorly. Beaks small, scarcely elevated above 

 the hinge-line, situated a little more than one-fourth the length 

 of the shell from the anterior extremity. Valves nearly regularly 

 convex from the dorsal to the ventral margin, the slope to the 

 cardinal margin usually a little more abrupt ; the anterior extrem- 

 ity of the shell compressed, with two obscure, sometimes obsolete 

 plications extending obliquely forward and downward from the 

 beak. In the casts a strong furrow pa.sses from the beak down- 

 ward towards the ventral margin, with a slight posterior ob- 

 liquity, growing shallower below and becoming obsolete at a point 

 about three-fourths the height of the shell from the dorsal mar- 

 gin. Surface of the casts marked by more or less inconspicuous 

 concentric lines of growth. 



Remarks. — This is a strongly marked species which cannot be 



mistaken for any other in the New Jersey Cretaceous faunas. 



The strong furrow extending downward from the beak in the 



casts represents a thickened rib upon the inner surface of the 



40 PAL 



