180 MYTILID^. 



terior outline, by the freedom or crampedness of their dwelling- 

 places. 



The shell is covered with a thin brownish yellow or scorched 

 looking epidermis (with a lustre more or less resinous), beneath 

 which the surface is concentrically painted with more or less 

 interrupted bands of a sombre violet or dusky liver-colour on 

 a paler ground. These markings are occasionally obsolete, and 

 sometimes partially transmuted into flexuous radiating streaks. 

 The interior is rich purple, or pearly white with purple stains. 

 The exterior is sculptured with most numerous radiating striae, 

 which are elevated, subcrenated, slightly divergent, and of nearly 

 equal strength throughout, except that they attenuate a little 

 in front, and usually become obsolete near the byssal aperture. 

 The interstices are about the width of the costellar striae, and 

 are restrained from dilating by the continual bifurcation of the 

 latter. The beaks are not perfectly terminal. The hinge has one 

 or two small teeth in each valve. The margin is crenated, 

 except near the byssal gape. 



The general shape is very irregular ; typically it is subtri- 

 angular, with the dorsal edge straightish, much elevated, and 

 nearly equal in length to the distance to the hinder extremity, 

 the subcentral dorsal angulation being well marked ; occasionally 

 it is crescent-shaped, the dorsal edge being curved and uniting 

 to the posterior margin without angulation. The convexity is 

 usually moderate ; when the valves have free scope for dilation, 

 then trifling ; when they are contracted and narrow, then con- 

 siderable. 



M. cRENATus, Lamarck. 



Mytilus erenatus. Lam. Anira. s. Vert. (ed. Desh.) vol. vii. p. 39. — Willcox, 

 Zool. Journ. vol. i. p. 590 ; Report Brit. Assoc, vol. iii, — 

 Brown, Illust. Conch. G. B. p. 77, pi. 23, f. 1, 2. — 

 SowERBY, Genera Shells, Mytilus, f. 3. — Reeve, Conch. 

 Iconica, pi. 102, f. 3. — Hanley, Recent Shells, vol. i. p. 244. 



Encyclopedie M^thodique, Vers. pi. 217, f. 3. 



An inhabitant of New Zealand, &c. ; introducedhy Mr. C. Will- 

 cox as naturalized at Portsmouth, having originally come over 

 attached to the " Wellesley'" from Bombay, and thence spread to 

 various parts of the harbour. We Jcnow of no good description of 

 this species (which is most closely allied to Magellanicus), but the 



