THRACIA. 39 



Habitat : Cornwall, Devon, and Dorset ; procured 

 by trawling. The reputed Irish localities are doubtful : 

 this species has been often mistaken for the adult of 

 T. pajjyracea : the only specimen in Mr. J. D. 

 Humphreys^s extensive collection of shells from Dublin, 

 Cork, and Bantry was marked by him '' England.^^ Mr. 

 Grainger obtained it in a dead state at Belfast, where 

 it is also found in a post-pliocene deposit, as well as in 

 the Coralline Crag. The foreign localities of which I 

 am assured are Morbihan (Mace and Tasle) ; Provence 

 (Martin) ; Gibraltar, 8 f. (M'^ Andrew) ; and ^Egean, 

 70 f. (Forbes) . Philippi has recorded it as recent at 

 Naples (on the authority of Scacchi) and fossil at 

 Palermo. 



My largest specimen is 2 J inches long, and 3 J broad. 

 The young have the same characters as the adult, and 

 are even more unlike T. papyracea. 



The Mya decUvis of Pennant, to which it was at one 

 time referred, appears to have been the half-grown state 

 of M. truncata. The present species is the Anatina 

 myalls of Lamarck, and T. Montagui of Leach. 



4. T. convex'a*, W. Wood. 



Mya convexa, W. Wood, Gen. Conch, i. p. 92, pi. 18. f. 1. T. conveaa, 

 R &H. i. p.229, pl.xvi. f. 1,4. 



Shell nearly rectangular, extremely gibbous, except towards 

 the front and posterior side, which are compressed to such an 

 extent as to give a wedge-like aspect ; it is thinner than T. 

 puhescens, opaque, and somewhat glossy : sculpture much finer 

 than that of the last species, and consisting of minute papilla^, 

 which are equally disposed over the whole surface in transverse 

 and undulating lines ; the marks of growth are slight, but 

 numerous : colour pale yellowish-brown : epidermis membra- 

 nous and thin : margins rounded on the anterior side and in 



* Convex. 



