398 Eocene Fossils of the United States. 
or more direct ; the tooth which is anterior to the fosset is double, 
and before it there is a minute pit; posteriorly, the hinge has a 
narrow elliptical depression or lunule, which gives the shell the 
appearance of a lateral tooth. 
. CorBULA. 
Corbula of Lamarck is a very ancient genus. I found one spe- 
_eies in the Silurian rocks of New York. Others occur in the 
Carboniferous limestones of Europe, in the Lias, Oolite, green 
sand and Gault. In the Tertiary, Deshayes enumerates thirty 
five species. Ihave not observed the genus in the Cretaceous 
strata of this country. I find two in the Hocene, and four in the 
Miocene. One recent species inhabits the coasts of Massachusetts 
and the Carolinas, (C. contracta, Say,) which occurs also in the 
Post-pliocene of Maryland; and another recent species I obtained 
from a sounding lead in deep water in the Gulf of Mexico. 
oe as NASUTA. Ovate-trigonal, ventricose, concentrically 
‘ medial; posterior extremity of larger valve ros- 
trated, ihe extremity opligeety” truncated ; umbonial slope of 
both valves carinated. (Plate IV, fig. 4.) 
— nasuta, Con.; Foss. Shells of Tert. Form., p. 38, Aug. 
C. Alabamiensis, Lea; Cont. to Geol., p. 45, plate i, fig. 12, 
Dec. 1833. 
Claiborne, Alabama. 
The valves of this common species are nearly schema convex, 
and the strize on both valves about equal i in size and approximate. 
In some specimens the basal margin is slightly contracted. The 
valves are suddenly rounded or curved inwards towards the base. 
Corsvta oniscus. ‘Triangular, profoundly ventricose, larger 
valve with concentric acute prominent strie, profound on the 
back, obsolete towards the extremities ; ainbonial slope carinated, 
terminal, the posterior slope or area Being profoundly depressed 
and ervey posterior end suddenly rostrated, rostrum reflected, 
extremity troneatedl lesser valve with numerous concentric 
wrinkled lipptosiitate lines, and carinated near the posterior eX 
tremity ; beaks submedial. (Plate IV, fig. 3.) 
C. oniscus, Con. ; Silliman’s Amer. Jour. of Science, vol. xxiii, 
P. 342, Jan. 1833. Bue Cont. to Geol., plate i. 
Claiborne, Alabama ; Washita river, Louisiana. 
