THR ACI A. 



Plate II. 



Species 7. (Fig. a, b, c, Mus. Cuming.) 



Thracia plicata. Thr. testa ovatd vel oblongo-ovatd, 

 subpapyraced, valvd sinistra depressd, postice concavo- 

 angulatd et declivi-truncatd, dextrd gibbosiusculd, am- 

 babus granoso-scabrosis et concentrice elevato-striatis, 

 oblique corrugato-plicatis, plicis antice fortioribus, pos- 

 tice gradatim evanidis; albd, ad marginemferrugined. 



The plaited Thracia. Shell ovate or oblong-ovate, 

 somewhat papyraceous, left valve depressed, poste- 

 riorly concavely angled and slopiugly truncated, right 

 valve rather gibbous, both granosely scabrous and 

 concentrically elevately striated, oblicpjely wrinkle- 

 plaited, plaits stronger anteriorly, posteriorly gra- 

 dually vanishing ; white, rusty at the margin. 



Deshayes, Eucyclop. Methodique, vers, vol. iii. p. 1039. 



Hab. West Indies (St. Thomas's Island) and California. 



Of this species, which M. Deshayes describes as living 

 probably in the seas of Senegal. Mr. Cuming possesses 

 specimens from California, and the Island of St. Thomas, 

 West Indies ; and they vary in form from oblong to ovate, 

 after the manner of the specimens a, b, c, selected for 

 illustration. They are of light, papyraceous, milk-white 

 substance, wrinkle-plaited across the front and central 

 parts of the shell, according to a type of structure which 

 has its highest development in T. maguijica from the same 

 geographical province. 



Species 8. (Mus. Cuming.) 



Thracia phaseolina. Thr. testa oblonga, subconvexd, 

 tenui, fragili, postice concavo-angulatd, subtruncatd. 

 antice attenuato-ovali ; concentrice teuuistriatd ; albd, 

 subniteute, vix scabrosd. 



The little boat Thracia. Shell oblong, slightly con- 

 vex, thin, fragile, posteriorly concavely angled, sub- 

 truncated, anteriorly attenuately oval ; concentrically 

 finely striated ; white, comparatively shining, scarcely 

 scabrous. 



Amphidesma phaseolina, Lamarck, Anim. sans vert. vol. vi. 

 p. 129. 



Mya declivis, Turton. 

 Anatina declivis, Turton. 

 Thracia phaseolina, Kiener. 

 Odoncincta papyracea, Da Costa. 



Hab. British seas and West Mediterranean. 



T. phaseolina has a much wider and more northerly 

 range ihan either of the larger Thracia of Britain. It 

 inhabits the European seas from Cornwall to the Shetland 

 Islands and from Norway to the Levant. 



Species 9. (Mus. Cuming.) 



Thracia villosiuscula. Thr. oblongo-ovatd, subcon- 

 vexd, tenui, fragili, postice concavo-angulatd, declivi- 

 truncatd, antice subirregulariter rotundatd; concen- 

 trice null: striata, albidd, minute scabrosd. 



The downy Thracia. Shell oblong-ovate, rather convex, 

 thin, fragile, posteriorly concavely angled, slopiugly 

 truncated, anteriorly rather irregularly rounded; con- 

 centrically rudely striated, whitish, minutely sca- 

 brous. 



M'Gillivray, Edin. Phil. Journ. p. 370. pi. 11. f. 6. 

 Thracia ovata, Brown. 



Hab. South and North Britain. 



Chiefly distinguished from the preceding species by its 

 more opaque scabrous texture, ruder striation, and more 

 uncouth broader growth. The downy epidermis is common 

 to many species of the genus. 



Species 10. (Mus. Cumiug.) 



Thracia pubescens. Thr. testa oblongo-ovatd, subrequi- 

 lateruli, valvd sinistra depressd, postice late angulatd, 

 ambabus truncatis, antice declivi-rotundatis ; sordide 

 albd, granoso-scabrosd, epidermide indutd. 



The pubescent Thracia. Shell oblong-ovate, nearly 

 equilateral, left valve depressed, posteriorly broadly 

 angled; both valves truncated, anteriorly slopiugly 

 rounded; dead-white, granosely scabrous, covered 

 with an epidermis. 



Mya pubescens, Pulteney in Hutchin's Dorset, p. 27. 

 Mya declivis, Donovan. 

 Anatina Myalls, Lamarck. 

 Anatina pubescens, Turton. 

 Thracia pubescens, Leach. 

 Thracia declivis, Brown. 



Hab. South-west coast of England. 



Messrs. Forbes and Hanley remark of Thracia pubescens, 

 " It is by no means improbable that Pennant's Mya de- 

 clivis was identical with this species ; at least, Montagu 



November, 1859. 



