MYTILUS. 9] 



Family — Mytiltd.e, Lamarck. 



Genus — Mytilus, Linnseus, 1758. 

 (' Syst. Nat., ed. 10, p. 704. ') 



Mytilus in^equivalvis, Soiverhy, 183G. Plate XV, figs. 7 a — d. 



183G. Mytilus invKquivalvis, J. de C. Sowerhy. Trans. Geol. Soc, ser. 2, vol. iv, 



pp. 241, 342, pi. xvii, fig. 10 {non Desliayes, 

 1838). 



1854. — — J. Iforris. Cat. Brit. Foss., ed. 2, p. 215. 



Description. — Shell slightly inequivalve, compressed, triangular, expanded and 

 rounded posteriorly; edges sharp except at the anterior part of the ventral 

 margin. Dorsal margin slightly curved, ventral nearly straight. Umbones slightly 

 curved, pointed ; no carina ; greatest convexity between the umbones and the 

 postero-ventral extremity. Surface smooth except for faintly marked growth- 

 lines. 



Measurements : 



(1) (2) 



Umbo to postero-ventral extremity . . 42 . 31 mm. 



Height (at right angles to greatest length) . 24 . 19 „ 



Thickness 13-5 . 11 „ 



(1), the Type; (2), in the British Museum. 



Affinities. — This species seems to approach M. Galliennei, d'Orbigny,^ but is 

 more compressed near the postero-ventral edge, less regular in outline, and without 

 ornamentation near the ventral border. 



Type. — In the Bristol Museum. The only other specimen seen is in the British 

 Museum. 



Distribution. — Blackdown Greensand. 



Mytilus, sp., cf. tornacensis, d'Archiac, 1847. 



1847. Mttilus tornacensis, A. (VArchiac. Mem. Soc. geol. France, ser. 2 



vol. ii, p. 307, pi. XV, fig. 3. 

 1847. — HAiNOENSis, P. de Byckholt. Elucubrat. paleont. (not seen). 



1 'Pal. Fran9. Terr. Cret.,' vol. iii (1844), p. 273, pi. cccxxxix, figs. 1, 2. See also Greinitz, "Das 

 Elbthalgeb. in Sachsen " (' Palaeontographica,' vol. xx), pt. 1 (1873), p. 213, pi. xlviii, figs. 1—3, 



