MYTILUS. 183 



name. I apprehend that it is the same as A. edentula, Say, and 

 A. areolatus, Swainson. If there be any difference among them, it 

 is that our shell is less compressed, less radiated, and less fragile 

 than A. edentida. The hhige is the same, and the areole before the 

 beaks is produced by a wave-like digression of the right valve to 

 form a peculiar tooth. The young shells are thin, and much more 

 radiated than the old ones, and the size of adults is seldom more 

 than two thirds of the dimensions above given. It is one of the 

 connecting links between Alasmodon and Anodon. 



Family MYTILIDtE. 



Hinge with the ligament marginal, partly included, linear, ex- 

 tending along a great part of the posterior border. Shell rarely 

 foliated ; adheres by a byssus. 



Oeniis IWYTILUS, Lin. 1758. 



Shell elongated, sub-triangular ; beaks terminal, pointed, straight; 

 hinge generally toothless ; muscular impression elongated, club- 

 shaped. 



Mytilus edulis. 



Fig. 82. 



Shell ovate-triangular, beaks terminal and pointed, basal margin straight, liga- 

 ment margin straight; posteriorly widened and rounded; hinge with a few den- 



ticulations; epidermis dark-bluish, shell violet beneath. 



» 

 Mytilus eduh's, Lin. Syst. Nat. 1157. — G.melin, Syst. 3353. — Turton ; Lin. iv. 291. 



— Chemn. Conch, viii. 169, t. 84, fig. 750. — Pennant, Brit. Zool. iv. 236, t. 66, 

 fig. 2. — MoNT.\GU, Test. Brit. 159; Lin. Trans, vi. t. 18, figs. 13, 14. — Dillwyn, 

 Catal. 309. — Turton, Conch. Diet. 109; Brit. Biv. 199, pi. 15, fig. 1 (peUucidus) . — 

 Deshayes, Encyc. Me'th. Vers. iii. 562, pi. 218, fig. 2. — Knorr, Vergn. iv. pi. 15, 

 fig. 4. — Lam. An. sans Vert. vii. 47. — Gualt, Test. t. 91, fig. E. — Donovan, 

 Brit. Shells, ii. t. 128. — Wood, Index, pi. 12, fig. 21. — Fleming, Brit. Anim. 411. 



— Adams, Gen. ii. 510, pi. 121, fig. 1. — Moller, Ind. Moll. Gr. 19. — Gould, 

 Inv. 121, fig. 82. 



Mijtilis vuhjaris, Da Costa, Brit. Conch. 216, t. 15, fig. 5. 



Miisculus subccerideus, Lister, Conch, t. 362, fig. 200. 



Mijtilus horeah's, Lam. An. sans Vert. vii. 46. — De Kay, N. Y. Moll. 182, pi. 13, fig. 222. 



— Middend. Moll. Ross. 15, 27. 



Shell triangular-ovate, solid, coarse, shining ; beaks pointed, 

 placed at one end, and slightly diverging ; basal or anterior mar- 

 gin generally straight, sometimes slightly convex, and sometimes 

 excavated ; hinge-margin rising in a straight line unites with the 



