ACEPHALA TESTACEA. 405 



Mytilus, Lin. 



The true Mytili or Sea-Muscles have a closed shell, with equal, 

 convex and triangular valves. One of the sides of the acute angle 

 forms the hinge, and is furnished with a long, narrow ligament. 

 The head of the animal is in the acute angle; the other side of the 

 shell, which is the longest, is the anterior one, and allows the pas- 

 sage of the byssus; it terminates in a rounded angle, and the third 

 side ascends towards the hinge, to which it is joined by an obtuse 

 anglej near this latter is the anus, opposite to which the mantle forms 

 an opening or small particular tube. The animal — Callitricihe, Poll, 

 has the edges of its mantle provided with branched tentacula near 

 the rounded angle, as it is there that the water enters required for 

 respiration. Before, and near the acute angle is a small transverse 

 muscle, and a large one behind, near the obtuse angle. Its foot re- 

 sembles a tongue. 



In the true Mytili the summit is close to the acute angle. 



Some of them are striated and others smooth. 



Myt. edulis, L. This common Muscle is frequently seen sus- 

 pended in extended clusters, along the whole coast of France, 

 to rocks, piles, Sec. Sec. It forms a considerable item of food, 

 but is dangerous if eaten to excess(l). 



Some of them are found fossil(2). In the 



Modiolus, Lam. 



Separated from the Mytili by Lamarck, the summit is lower and 

 near the third of the hinge. This summit is also more salient and 

 rounded, approximating the Modioli more closely to the ordinary 

 form of the bivalves(3). We may also separate from the Mytili the 



(1) Add Mytilus harbatus, L., Chemn., VIII, Ixxxiv, 749; — M. angulatus, lb., 

 756;— if. bidens, lb., 742, 745;— M. afer, lb., Ixxxiii, 739— 741;— i»f. smaragdinus, 

 lb., 745; — M. versicolor, lb., 748; — M. lineatus, 753; — M. exustus, lb., 754; — M. 

 striatulus, lb., 744; — M. Ulocularis, lb., Ixxxii, 736; — M. vulgaris, lb., 732; — M. 

 sexatilis,n\\m^\i.,M\xs. xlvi, Ji ;—M. fulgidus, Argenv., xxii, D; probably the 

 same as the Mija perna, Gm., Chemn., VIII, Ixxxiii, 738; — M. azureus, lb. H; — 

 M. murinus, lb., K;—M. puniceus, Adans., 1, xv, 2;—M. niger, lb., 3;—M. Ixvi- 

 gatus, lb., 4, &.C.: some of these, however, may be mere varieties. 



(2) M. Brongniart has formed them into a subgenus by the name of Mttiloida, 

 Ap. Cuv. Oss. Foss. tome II, pi. iii, f. 4. 



(3) Mytilus modiolus, Chemn., VIII, Ixxxv, 757—760, and that of Mull., Zool. 

 Lan., II, Iii, which appears to be another species; — M. discors, Chemn., VIII, 

 Ixxxiv, 764— 768;— M. testaceus, Knorr., Vergn., IV, v, 4, &c. 



