208 PALEONTOLOGY OP NEW JERSEY. 



ARCID^. 



Genus AECA Liun. 



Area quindecimradiata. 



Plate XXVII, Figs. 10-13. 



Area quindecemradiata Gabb. P. A. N. S., ISCO, p. 95, Plate II, Pig. 2. Synopsis, p. 



97. Meek, Check-list, p. 9. 

 A. ? (Gabb) Meek. Geol. Surv. N. J., 1868, p. 725. 



Shell below a medium size, very inequilateral, transverse, and extremely 

 ventricose, with large, tumid, projecting beaks, situated anterior to the mid- 

 dle of the length ; sliglitly enrolled and very distant, leaving a very broad 

 flattened cardinal area, even in the internal casts. Hinge-line nearly as long 

 as the shell. Posterior margin obliquely truncate and the anterior end rap- 

 idl}^ receding from the extremity of the hinge-line, passing with an almost 

 regular curvature into the very broadly curved basal line ; posterior basal 

 angle obtusely jjointed and situated near the lower side. On the casts the 

 projecting keel, formed along the junction of the valves by the thickening 

 of their borders, is very distinctly marked. Muscular imprints moderately 

 large and well marked ; no distinct ridge borders the posterior one, but the 

 cast shows evidence of a decided thickening. Surface of the cast showing 

 evidence of a few strong radiating ribs, tlie exact number undeterminable. 



The casts of this species are very well marked, and are not readily 

 confounded with those of any other species. In the transverse form they 

 correspond with Idonearca transversa, but the muscular ridge does not aj)- 

 pear ; the beaks are larger and more distant and the valves more ventri- 

 cose. The largest specimens which I have observed do not exceed one 

 inch and one-quarter in extreme length. 



Formation and localities. — Mr. Gabb cites his specimens as coming from 

 MuUica Hill, New Jersey. All others which I have seen are from the base 

 of the Upper Marls near New Egypt, New Jersey, and were mostly oIj- 

 tained by Dr. N. L. Britton. Others were in the old collections of the State 

 Survey, and are marked as from John Iron's pits, near New Egypt, and 

 are from the same horizon. 



