LAMELLIBRANOHIATA OF THE LOWER MABLS. 171 



plomya ellipiica, which I think ought also to be placed under the genus 

 Corimyaj but they are never so ventricose and never so much constricted 

 behind the beaks as are casts of that species, so that their triangularly- 

 elliptical outline will always readily distinguish them. They also bear 

 considerable resemblance to casts of Linearia metastriata Conrad, from 

 which it will be difficult to distinguish them if ever found associated. The 

 slope of the cardinal margin and the impressed groove bordering the mus- 

 cular impression, as well as the inequality and twisting of the valves, will be 

 a guide in determining their relations. There can be no question, I think, 

 about the generic reference of the species, as they correspond in every par- 

 ticular with both description and figures of the species referred by Prof. 

 Agassiz to his genus Corimya. 



Formation and locality. — In the Lower Marl Beds, Upper Freehold, col- 

 lected by Dr. Bruere, and at Marshallville, Salem County, New Jersey. I 

 have also seen quite a number of these casts in the collection of the Academy 

 of Natural Sciences, Philadelphia, from several localities. 



DONACINID^. 



Genus DOXAX Linn. 



Donaz Fordii. 

 Plate XXIII, Fig. 1. 

 Bonax Fordii Conrad. Am. Jour. Conch., Vol. Y, p. 102, PI. IX, Fig. 27. 



Shell below a medium size for the genus, triangularly cuneate, very 

 inequilateral, the anterior end being nearly twice as long as the opposite. 

 Valves ventricose, the extremities sharply rounded, the anterior broadest at 

 the end. Surface of the shell poHshed and marked by fine radiating im- 

 pressed lines, which strongly and deeply crenulate the margin of the shell. 



This shell is so exactly a representative of the Hving species common 

 along the Atlantic coast that it would be extremely hazardous to its specific 

 distinction to institute comparisons. The specimen is very imperfect in 

 form, having had the beaks crushed in and the shell partially exfoliated ; 

 but the characters are sufiiciently preserved to establish at once its relations. 



