FAMILY MYTILIDZ — MYTILUS. 183 
MytiLus PELLUCIDUs. 
PLATE XXIV. FIG. 256. 
Mytilus pellucidus, PENNANT, Br. Zool. Vol. 4, p. 237, pl. 66, fig. 3. 
M. id, Turton, Conchol. Brit. Ins. p. 197, pl. 15, figs. 1 and 2. 
M. edulis, var. pellucidus, GouLp, Invertebrata of Mass. p. 122. 
Description. Shell oblong, convex, pellucid, smooth, with very minute concentric wrinkles ; 
anterior margin in young specimens nearly straight, more curved with age. Beaks small, 
approximated, scarcely terminal, occasionally with two or three teeth, but these are more often 
wanting: posterior margin produced and more or less angulated. 
Color. Light horn-color or yellowish, but more usually dark horn, with vertical blue radia- 
tions, most conspicuous when held against the light; as the animal increases in size, these 
radiations become more numerous. Within a rich ultramarine blue, particularly towards the 
margins. 
Length, 0°4-—1°2. Width across the beaks, 0°6 - 2°1. 
Tn very young specimens, the surface of the valves is furnished with scattering hairs, and 
the basal margin is lineated. As the genera Mytilus and Modiola now stand, it is doubtful 
in many specimens to assign its true position. 
(EXTRA-LIMITAL.) 
M. incurvatus, Lam. Shell oval, thick, opake, tumid, much incurved on the anterior side: beaks 
divaricate, with two or three teeth only under them. Color, bluish grey. Length, 1+4. An 
var. M. borealis? Northern shores of Europe and America. 
M. ungulatus, Linn. Shell oblong, ventricose, roughened with transverse plaits, curved on the anterior 
side, and the summits conical and diverging: hinge with from three to five minute teeth. Color: 
epidermis blackish or purple; in the young, the epidermis green, and occasionally with reddish 
zigzag lines. Length, 4°0-5-+0; width, 2-0-2+4. Coast of Europe and America. 
M. cubitus. (Say, Ac. Sc. Vol. 2, p. 263.) Shell oblong, striated, with elevated subglabrous lines 
which are smaller on the anterior side: anterior edge linear or slightly concave ; posterior edge 
ascending from the base in a right line to a prominent posterior angle, which is rather behind the 
middle of the shell, from which it descends by a concave line to the obliquely and very obtusely 
rounded tip. Color, yellowish, polished, and somewhat fasciated with green or brownish, disap- 
pearing on the anterior margin. Length, 1-2; breadth, 0°5. Seacoast. 
M. lateralis. (Iv. Ib. p. 264.) Shell transversely oval, inflated, subpellucid, with numerous concentric 
wrinkles: anterior and posterior margins longitudinally ribbed, and crenating the basal margin; 
intermediate area without longitudinal lines: the most prominent part of the shell extending from 
the beak to the tip of the anterior margin, and bounded on its posterior side by an indented line. 
Color : epidermis pale brown. Length, 0°3; breadth, 0°5. Southern coast. 
M. hamatus. (Ip. Ac. Sc, Vol. 2, p. 264; Am. Conch. pl. 50. M. striatus, Barnes, Am. Jour. 
Vol. 6, p. 364.) Shell very much contracted and incurved at the base, which is acute. Valve 
