TRIBE MYTILACEA. 249 



M. Ungularis. Lam. 23. — E. t. 216. /. 3? — Semiovate, ante- 

 riorly dilated, rather thin, angulated and compressed ; posterior 

 edge nearly straight but slightly bulging out towards the ventral ; 

 epidermis blackish with a larger or smaller portion tinged with ful- 

 vous ; beaks small. 3. India and New Holland. The specimen in 

 the museum at Paris has the hinge margin short and straightish. In 

 all probability the next species, (judging from the original specimens) 

 is no more than a depressed variety of this shell. 



M. Planulatus. Lam. 24. Ovate rhombic, rather depressed, 

 in part blue, part white, at the beaks acute ; angle of the anterior 

 side, central. 3. New Holland. 



M. Bore alls. Lam. 25 — M. Edulis. Goidd.Mas.f. 82. Oblong, 

 thick, rather tumid, bluish or purplish white, under a black epider- 

 mis ; hinge margin rather long, forming an arch but never a distinct 

 angle with the anterior ventral margin : posterior margin nearly 

 straight, neither incurved nor flattened : beaks not approximate, 

 inclining inwards, divergent : interior dark blue, white towards the 

 obtuse beaks , hinge with a few denticles. Newfoundland, N. Ame- 

 rica. 1|..3|. Allied closely to Edulis, but I think distinguishable 

 by the above characters. In adult typical specimens of our common 

 mussel, the anterior margin is subparallel to the posterior ; in Borealis. 

 the shell being dilated anteriorly, this is by no means the case. It 

 is likewise broader, with the surface less compressed both anteri- 

 orly, and posteriorly . The anterior ventral margin is well arcuated. 



M. Angustanus. Lam. 26. Narrow-oblong, subarcuated, ob- 

 tusely angulated, bluish, the beaks inflected. \\. "Shape of 

 Edulis without its posterior swell : two small teeth." 



M. Corneus. Lam. 27. Oblong, thin, yellowish horn-colonr, 

 obscurely rayed, anteriorly curved ; posterior side straight : with 

 a brown spot. If. 



M. Galloprovincialis. Lam. 28. — Phil, p. 12. t. 5.f. 12, 13. 

 Ovate-triangular, bluish-black, anteriorly much compressed, the 

 striae of growth strong and the epidermis usually glossy: dorsal 

 margin straight and rather long, forming an obtuse but distinct 

 angle with the anterior ventral, and thence sweeping in an uninter- 

 rupted curve to the ventral edge : posterior side depressed, white 

 but of a yellowish brown when covered by its epidermis, edge 

 nearly straight, very slightly incurved : much attenuated towards 

 the acute beaks : hinge with a few denticles. Mediterranean. 2\. 

 Variable in its breadth but easily to be distinguished from the next by 

 its longer dorsal margin and distinct angle. Theumbonal ridge is 

 more acute. 1 



1 The Dilatatus of Gray. ( W. S. t. 2. f. 2.) seerm allied to this 

 species. 



