6 GENUS THRACIA. 
upon the coasts of England, in the sands of Falmouth and Ply- 
mouth; it is found also in the Mediterranean. 
3. THRACIA PLICATA, Desnayves. The Plaited Thracia. 
(Collect. Mass. et Lasoir.) 
Pl. UI, fig. 3. 
Th. testa ovato-oblongd, transversd, wquilaterd, inequivalvi, depressa, 
transversim plicatd, alba, diaphana. 
Shell ovate, oblong, transverse, equilateral, inequivalve, in- 
flated, beaks small, that of the left slightly notched. The 
valves are white, delicate, and diaphanous, rounded upon the 
anterior side, truncated obliquely upon the posterior side: the 
side is bounded outwardly by an obtuse angle, which extends 
from the beak to the lower and posterior edges. ‘The exterior 
surface presents some very prominent transverse folds, round- 
ed, undulating, more or less numerous; the cardinal edge is 
straight, and presents upon each valve a small horizontal hol- 
low, triangular, not very thick, in which is confined a small 
internal ligament, which shows itself a little externally ; inter- 
nally the valves are white, and transversely plaited. The 
anterior muscular impression is very superficial, elongated, 
and very narrow ; the posterior rounded and small : it is unit- 
ed to the anterior by a palleal impression, deeply notched 
posteriorly. 
Length 1 inch 6 lines. Width 1 inch. 
Country unknown. 
* 
This species is rare in collections; it is very remarkable for 
its whiteness, and for the very prominent transverse folds upon 
the whole of the shell. 
