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 vei;y 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. Grabb's C. 

 Texana, from the Eocene of Texas, somewhat resembles it in its triangular 

 form, but is neither so elevated nor so short in proportion. 



Locality: Mr. 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. 



