BIVALVIA. 171 
1. ErYCINELLA ovaLis? Conrad. Tab. XV, fig. 10a—f. 
EryctIneLLa ovaLts? Conrad. Foss. of the Miocene Formation of the United States, p. 74, 
pl. xli, fig. 5, 1845. 
Goopattia? pyemzA. S. Wood. Catalogue, 1840. 
— ?crENATULA. Id. 
Spec. Char. Testd minutd, obliqud, ovato-trigonuld, inequilaterali, tumidd, crasst, 
concentrice striata; postice rotundatd, antice rectiusculd ; cardine bidentato ; margine 
ventrali crenulato. 
Shell minute, oblique, ovately triangular, inequilateral, tumid, thick and strong, 
concentrically striated ; posterior side rounded, anterior nearly straight; hinge with 
two teeth, ventral margin crenulated. 
Diameter, ;th of an inch. 
Locality. Cor. Crag, Sutton, and Gedgrave. 
This little shell is particularly abundant in the Coralline Crag at Sutton; and from 
its prominent dental apparatus and crenulated margin, the two valves may be often 
obtained in their natural position, giving thus an opportunity of observing the entire 
margins of the shell in juxtaposition, without the slightest appearance of any fulcrum 
or depression into which the ligament could have been inserted, so as to have become 
visible externally when the valves are closed, the two pieces locking so close together 
as to be with difficulty separated. The shell is thick and strong, with a prominent 
obtuse umbo, and the whole exterior, when in perfect condition, is covered with 
concentric ridges or rounded strie. The hinge of the right valve consists of 
two large teeth diverging from the umbo, having a triangular space between them, 
and a small obscure lateral tooth on both sides; in the left valve there are two 
large cardinal teeth also diverging, which lock into depressions on the outside of 
the teeth of the right valve; besides these two cardinal teeth in each there are two 
small denticles in the left, between which and the larger teeth are spaces for the 
reception of the two large teeth of the right valve, thus leaving in the centre a vacant 
space immediately beneath,the umbo, where it is presumed the ligament was inserted ; 
and in this valve also are two lateral teeth, the one at the extremity of the slope of the 
anterior margin is prominent, fitting into a corresponding depression in the anterior 
margin of the right valve, while on the other side it is the reverse, corresponding in 
this character with the lateral teeth of the small species of Asfarte, to which it is 
evidently nearly related. The edge of the margin is deeply denticulated in the adult 
shell, but in the immature state it is perfectly smooth; the adductor muscles are 
deeply impressed, large, and of an ovate form, situated near the extremity of the 
lateral teeth ; they are connected by a simple mantlemark, without the least inflection : 
in the young state the teeth of the hinge are comparatively larger than when full 
grown, and the margin is then without crenulations; from these, with some other minor 
differences, it was thought to be a distinct species, but a better examination and more 
specimens give reason to believe it to be only the immature state. 
