Mvtjlus. MOLLUSCA. MYTILIDjE. 411 



MYTILIDiE. 



Gen. CIII. MYTILUS. Mussel.— Shell longitudinal, equi- 

 valve, beaks acute, nearly straight and terminal, with a va- 

 riable number of minute teeth. 



•—417. M. edulis. Common Mussel. — Beaks blunt, ventral 

 margin towards the beaks swollen ; smooth, or slightly wrinkled 

 by the layers of growth, with longitudinal coloured bands. 



Musculus subcoeruleus, List. Conch, t. ccclxii. f. 200 Myt. edulis, Linn. 



Syst. i. 1 1 58 — Gregarious on hard ground, above low water-mark. 

 Sometimes reaching to 5 inches in length, and 2 in breadth ; colour bluish- 

 black, with dusky, yellowish, radiating lines ; inside whitish, with blue mar- 

 gins ; hinge with many teeth. When of slender growth and translucent, it 

 has been denominated Mytilus pellucidus ; and when, by confmement~in rocks, 

 the beaks have become incurved, with the anterior margin concave, it has 

 then been called M. incurvatus. The mussel is extensively used as a bait ; 

 and is likewise sought after as an article of food, being esteemed rich and in 

 season in autumn, but useless and even deleterious in spring. 



418. M. decussahts. 



" Shell longitudinally ovate, with the umbo at the smaller end ; sides 

 equal. It is very thin, pellucid, of a pearly white, when divested of the epi- 

 dermis (which is a pale olive-brown), and is finely striated longitudinally, 

 crossed by more minute strise in a transverse direction, that gives it a decus- 

 sated appearance when examined under a microscope. The inside is smooth, 

 with a nacred gloss. At the hinge is a slight indenture, and the margin 

 contiguous slightly denticulated ; and near the front margin is a singular re- 

 flected transverse ridge." — Mont. Test. Brit. Sup. G9. A minute shell, about 

 the eighth of an inch in length, found by Mr Laskey, at Dunbar ; its place 

 in the system uncertain. 



STRAGGLERS. 



1. M. umgulatus — Smooth, hind margin'inflected ; hinge with two teeth; 

 greenish, with transverse zig-zag markings, List. Conch, t. ccclx. Don. Brit. 

 Shells, t. cxxviii. f. 2.— Adhering to the bottom of vessels, especially from 

 the African coast. 



2. M. polymorphic, Gm Ventral surface flattened ; dorsal edge rounded; 



beaks obtuse and inflected; green, with dusky transverse bands. Sower. 

 Zool. Journ. i. 584. — Found in the Thames, in the Commercial Docks, into 

 which it is supposed to have been brought from the Danube with timber. 



3. M. crenatus. — Trigonally ovate, with slightly wrinkled, longitudinal, 

 rounded ribs. This species was brought into Portsmouth Harbour, 3d May 

 181G, on His Majesty's ship Wellesley, from the East Indies. A specimen now 

 before me, taken at that time, is nearly three inches in length. It appears from 

 a communication by Lieutenant J. H. Davies and Mr Willcox (Annals of 

 Philosophy, Aug. 1825, 148), that it had survived since 181G, and had propa- 

 gated — These two species differ from the true Mytili in the anterior adduc- 

 tor muscle, being seated in a pit at the beak. 



