MIOCENE MOLLUSCA AND CRUSTACEA. 87 
The specimens of this species which I have seen are generally of small 
size, the largest one being within half an inch in height, and of less length. 
The form is triangularly ovate in outline, slightly inequilateral, and much 
inflated, both valves being quite ventricose; the beaks are large and very 
gibbous, that of the deeper valve much the largest. Umbonal ridge dis- 
tinct in each valve, but not strongly marked. Surface of the valves variable 
in their markings, usually with impressed concentric lines, but sometimes 
developing concentric ridges more or less rounded, but indistinct on the 
umbonal slope. Some of the best preserved and larger specimens show 
obscure radiating lines on the surface of the larger valve, but I have not 
observed them on.any of the smaller valves. Most of the examples have 
lost the external layer of shell. In the interior the ligamental pit of the 
larger valve is very large and deep, excavating the inner face of the beak in 
most instances. The tooth is also very large and strong. 
I am somewhat in doubt as to the existence of the “concentric impressed 
lines” on the external surface of the shell of this species mentioned by Mr. 
Conrad. They undoubtedly exist, but I think only on the inner layers. I 
have seen but one valve which appears to me to possess the external layer, 
and that has rounded folds like the majority of the species of Corbula. The 
species is remarkable for the elevated form of the shell, which is usually 
considerable higher than long, and often nearly equilateral. Mr. Gabb’s C. 
Texana, from the Kocene of Texas, somewhat resembles it in its triangular 
form, but is neither so elevated nor so short in proportion. 
Locality: My. Conrad’s type specimens were obtained on Stow Creek, 
near Shiloh, N. J. I have specimens from near the same locality from the 
National Museum collection, as well as what are supposed to be the types 
from the Academy of Natural Sciences, Philadelphia. 
