G E N U S T II R A C I A . 



upon the coasts of England, in the sands of Falraouth and Ply- 

 mouth ; it is found also in the Mediterranean. 



3. THRACIA PLICATA, DESHAYES. The Plaited Thracia. 



(Collect. MASS, et LAJOIE.) 



PI. II, fig. 3. 



Th. testa ovato-oblonga, transversa, sequilatera, insequivalvi, depressa, 

 transverslm plicata, 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. 



