41 
THRACIA, Leach. 
Gen. Char. Valves unequal, more or less gaping 
posteriorly; hinge without teeth, its ligament 
attached to a sunken narrow fulcrum, its car- 
tilage internal, bifid, seated between two thick 
equal processes or calli, one in each valve ; 
sinus in the attachment of the mantle short. 
A genus very properly separated by Dr. Leach from 
Mya of Linnaeus and other authors. The equality of the 
processes for the support of the hinge cartilage in the two 
valves being a very strong character ; near the beak there 
is a protuberance which may be considered as a rudimentary 
tooth, and above this protuberance the old shell is usually 
eroded. It has the strong epidermis of the Myaria and an 
opaque not pearly substance. 
The recent species inhabit muddy or sandy shores in 
temperate climates : a few only are known, and the fossil 
ones are scarcely more numerous ; they occur in the ter- 
tiary and newer formations. 
THRACIA pubescens. 
TAB. DCXXXL— jig. 1. 
Spec. Char. Transversely elongated, ovate, con- 
vex ; surface granular beneath the epidermis ; 
posterior extremity truncated, the truncation 
inclined towards the nearly straight ventral 
