MOLLUSCA. 541 



angular, and highly arcuate in its passage from the beaks to the 

 postero-basal angle of the valves. Cardinal border arcuate, the 

 cardinal and basal margins subparallel and nearly equally 

 curved; posterior margin squarely truncate below and sloping 

 toward the hinge-line above; anterior end sharply rounded, and 

 deeply excavated blenelath the beaks. Poistero-cardinal slope 

 rather abrupt. Surface of the shell, as indicated on the casts, 

 smooth or marked only by concentric lines of growth." (Whit- 

 field.) 



ReTnan'ks. — Morton's type of this species has. apparently been 

 lost or destroyed, and it has usually been the custom tO' consider 

 the species as a synonym of V. conradi. Whitfield, however, 

 has revived Morton's name, applying it to certain specimens 

 which, from the locality given, probably occur in the Horners- 

 town marl, but this can not be asserted with certainty because 

 the form has not been met with in the recent collections, and it 

 is not certain that the specimens used by Whitfield are specifically 

 identical with Morton's type. In its generic characters this 

 species, as interpreted by Whitfield, is evidently related to 

 Veniella rhomboidea, and as has been pointed out under the dis- 

 cussion of that species, both should perhaps be referred to the 

 genus Isoarca. 



Formation and locality. — Hornerstown marl ?, Blue Ball, and 

 near Mullica Hill (Whitfield). 



Geographic distribution. — New Jersey. 



Genus Et^a Conrad. 

 Etea carolinensis Conrad. 



Plate LIX., Figs. 4-6- 



1875. Btea carolinensis Con., Kerr's Geol. N. Car., App. p. 6, 



pi. I, fig. 14. 

 1905. Btea carolinensis Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 14. 



Description. — The dimensions of a shell of average size, pre- 

 serving both valves, are: length, 33 mm.; height, 22.5 mm.; 



