MONTACUTA. 77 



phreys), are among' its Irish localities. In Scotland, in 

 many of the lochs and other localities among the Hebrides 

 (Jeffreys and Barlee) ; Lamlash Bay, in Arran (Alder). 



The bidentata of Gould, does not exactly coincide (in 

 description, at least,) with our British species. 



M. SUBSTRIATA, MoiltagU. 



Very oblique ; with divergent elevated lines upon the uin- 

 bones. 



Plate XVIII. figs. 8 and 8 a, and (Animal) Plate 0. fig. 2. 



Mya substriata, Mont. Test. Brit. Suppl. p. 25 — Turt. Conch. Diction, p. 103. 

 — Wood, General Conch, p. 102. — Dillw. Recent Shells, 

 vol. i. p. 47. 

 Montacuta substriata, Turt. Dithyra Brit. p. 59, pi. 11, f. 9, 10. — Flem. Brit. 



Anim. p. 405.— Macg. Moll. Aberd. p. 303.— Brit. 



Marine Conch, p. 51. — Alder, Cat. Northumb. and 



Durham Moll. p. 96. 

 Erycina substriata, Recluz. Rev. Zool. 1844, p. 330. 

 TeUimya substriata, Brown, 111. Conch. G. B. p. 107, pi. 40, f. 23. 

 ? Sphwnia costulata, Macgilliv. Moll. Aberd. p. 301. — Brit. Marine Conch. 



p. 245 (copied). — Brown, 111. Conch. G. B. p. 133 



(copied). 



This little bivalve, which derives additional interest from 

 its peculiar habitat, is remarkably oblique in outline, very 

 thin, fragile, semi-transparent, extremely inequilateral, and 

 of a more or less oval shape. The valves are not ventricose, 

 but are moderately convex, the swell being generally dif- 

 fused over the upper portion, and diminishing gradually 

 and equally towards either extremity ; when fresh, they 

 are covered with a glossy yellowish (or colourless) skin, 

 beneath which the surface is pale or whitish. The exterior 

 is marked with radiating subdivergent elevated lines, which 

 are rather distant, not readily perceptible, and most ap- 

 parent upon the middle area : there is no other sculpture 



