MYTILUS. 183 



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

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

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

 than A. edentida. The hinge 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 

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

 connecting links between Alasmodon and Ariodon. 



^to 



Family MYTILID.E. 



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 MYTILUS, Lin. 1758. 



Shell elongated, sul>triangular ; beaks terminal, pointed, straight; 

 hinge generally toothless ; muscular impression elongated, club- 

 shaped. 



Mytilus ediilis. 



Fig. 82. 



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

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

 ticulations ; ej^idermis dark-bluish, shell violet beneath. 



Myttluft ednlk, Lin. Sj'st. Nat. 1157. — G.MibLix, Syst. 3353. — Turton ; Lin. iv. 201. 



— Chemn. Conch, viii. 169, t. 84, fig. 750. — Pennant, Brit. Zool. iv. 236, t. G6, 

 fig. 2. — Montagu, 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 {pellnnidn^). — 

 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. 



]\fjjti/is vuk/aris, Da Costa, Brit. Conch. 216, t. 15, fig. 5. 



^fllsculus subc.ctruleus, Lister, Conch, t. 362, fig. 200. 



Mytilus horealls. 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 



