Genus THRACIA, Leacu. 
THE THRACIA. 
Generic characters.. Shell ovate, oblong, transverse, ine- 
quivalve ; the beaks strongly recurved, that of the right valve 
notched to receive that of the opposite side; the right valve 
more convex and larger than the left; the hinge has upon 
each valve a horizontal and narrow nympheal callosity, which. 
sometimes expands into a spoon-shaped projection, and con- 
tains an internal ligament, which is prolonged, and slightly issues 
outwardly into the corselet. ‘Iwo muscular impressions, the 
anterior depressed, elongated, contracted towards its middle, 
and united to the posterior, which is rounded, by a palleal 
impression, strongly notched at its posterior part. 
Testa ovato-oblonga, transversalis, inequivalvis; natibus fortiter recur- 
vatis, dextre valve emarginata nate, que alterium excipiat; dextra valva 
ventricosior majorque sinistra: Cardo variabilis; in utrdque valva callum 
nymphale, horizontale, angustum, aliquando dilatatum cochledriforme ; 
Ligamentum internum, externé prominulum. Due impressiones muscu- 
lares; anterior depressa, producta, contracta ad medium, junctaque poste- 
riori; posterior rotundata impressione palleali, posticé largiter emarginata. 
The animal is oval, thick, enveloped in a very delicate 
mantle, diaphanous upon its sides, through which is distinctly 
seen the branchie and the abdominal mass; the edges are 
swollen, lobed, and united in almost the whole of the circum- 
ference, so that they present only three openings ; the first is 
found at the anterior and lower third of the median line, and 
Thracia. A 
