245 
and ventral margin. 0,58...1. Scotland. Isle of 
Man, $e. More delicate and more elongated than the 
young of M. Solida. 
Ervitia. PEtituctipA. Macg. Aber. p. 341.— 
Tewuina. P. Brown. Ill. Conc. t. 16. f. 22. Ovate- 
elliptical, compressed, very inequilateral, rounded at 
both ends, semitransparent, glossy, white, concentrically 
sulcated, dorsal line concave; hinge with two slender 
divaricate teeth separated by a triangular space. 0,04. 
...0,06. Aberdeen. 
Montacuta, GuaBRaA. Macg. Ab. p. 303.— 
Trevumya. G. Brown Ill. Con. ¢. 14. f. 19. Ovate- 
oblong, subelliptical, very thin, subpellucid, very 
inequilateral, nearly equally rounded at both ends, 
convex, white or tinged with brown, uearly smooth, 
slightly punctulate towards the margin; inside glossy, 
slightly granulated, somewhat irridescent ; in the right 
valve an oblique deflexed, adherent concave tooth, and 
a white sinus with a conical tooth, the margins chan- 
nelled fora short space ; in the left valve a sinus with a 
concave tooth, the margins plain. 0,25.—0,416. 
Aberdeen. 
SpH@nia Costunata. Macg. Aberd. p. 301. 
