178 SUPPLEMENT. 



curved; on the anterior side considerably expanding and 

 rounded ; on the back rising towards the anterior end : beaks 

 small, calyciform, blunt, prominent, incurved, but not having 

 any indentation below them; they are placed close to the 

 posterior side, which is shorter than the other side, and not 

 ^ of its size : hinge-line rectangular, occupying about ^ of the 

 circumference : cartilage as in 31. hidentata : hinge-plate nar- 

 row and strong, thicker in the middle, not excavated so deeply 

 as in the last-named species, and scarcely at all in the right 

 valve : teeth, in the right valve short, triangular, slightly in- 

 clining inwards, not widely separated ; in the left valve long, 

 erect, laminar, and parallel with the hinge-line ; the anterior 

 teeth are the largest in both valves : inside iridescent and 

 polished, very finely marked (more distinctly on the anterior 

 side) with slight lines which radiate from the beaks : scars 

 irregularly oblong, and conspicuous. L. 0*075. B. 0-1. 



Ha-bitat: Hebrides and Shetland, 40-80 f., in muddy 

 ground ; rare. E. Bohusliin (Lilljeborg) ! Smaller than M. 

 hidentata, and distinguishable by being narrower, not de- 

 pressed, but convex, having a glossy surface, and by the pos- 

 terior side being disproportionately small and abruptly trun- 

 cated ; that side in M. hidentata is invariably squarish, and 

 more or less angulated. The teeth in the right valve of M, 

 tumidida are much smaller than in the same valve of M. hi- 

 dentata, and are not so widely separated by the cartilage -pit ; 

 they are triangular and not leaf-like, and slightly incline in- 

 wards instead of being erect. 



P. 210. — M. FEERUGiNosA. F. Portrush (Portlock) ; Nor- 

 way and Monte Mario ! E. Norway, 5-50 f., and Greenland 

 (Sars) ; Arcachon (Lafont) ! ; Mediterranean (M' Andrew and 

 others) ! ; Adriatic (Brusina) ! ; Maderia (Watson) ! 



P. 216. — M. Dawsoni. Mr. Dawson has since dredged off 

 Cruden in the Moray Eirth two or three perfect specimens and 

 many single valves of this curious little shell. When quite 

 fresh they have a light yellowish green epidermis. In shape 

 and size this species resembles Kellia pumila of S. Wood from 

 the Coralline Crag ; but the hinge is essentially different. 



P. 216. — M. DONACiNA. I last year dredged another valve 

 (the left) in St. Magnus Bay, Shetland. Both valves 

 figured. 



