238 MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 



and covered with filaments projecting from the epidermis ; the 

 third area smooth and reddish-brown. The filaments have a 

 flat triangular base, not serrated. 



The animal has the mantle-lobes very thin, whitish, thick- 

 ened and reddish-orange at the margins ; the branchiae, which 

 are very large, also reddish-orange ; the foot very small, lingui- 

 form, grooved beneath, and of a brighter tint of the same; the 

 byssus attached to the base of the foot behind very large, 

 arising from a large, posteriorly grooved prominence, in the 

 form of a subulate cartilaginous shaft, from the anterior and 

 posterior sides of which arise very numerous horny filaments ; 

 the posterior adductor muscle extremely large and round, the 

 anterior very small and thin. 



Not uncommon ; seldom seen on the beach ; young indivi- 

 duals adhering to corallines, shells, and other matters, often 

 taken up by the lines from deep water, off Aberdeen. 



Mytilus Modiolus. Linn. Syst. Nat. i. 1158? — Mytilus barbatus. 

 Linn. Syst. Nat. i. 1156. — Modiola Modiolus. Turt. Brit. Biv. 199. 

 — Mytilus Modiolus. Mont. Test. Brit. 163. — Mytilus barbatus. 

 Mont. Test. Brit. 161. — Modiola vulgaris. Fleru. Brit. Anirn. 412. 

 — Modiola papuana. Lamk. Syst. vi. Ill ; Ed. 2. vii. 17. — Modiola 

 barbata. Lamk. Syst. vi. 114; Ed. 2. vii. 22. — Mytilus Modiolus. 

 Penn. Brit. Zool. iv. 113. PI. 66. f. 77; Ed. 2. iv. 238. PI. 69.— 

 Mytilus urnbilicatus. Penn. Brit. Zool. iv. 112. PI. 65. f. 76; Ed. 

 2. iv. 238. PI. 68.— Mytilus barbatus. Penn. Brit. Zool.; Ed. 2. 

 iv. 238. PI. 67. f. 2. 



2. Modiola discrepans. Compressed Ribbed Modiole. 



Shell ovate, compressed, opaque, with a brown or blackish 

 epidermis ; umbones rather tumid ; posterior end much 

 broader and rounded ; about eight broad grooves from the umbo 

 to the margin, in the middle a smoothish space, and behind a 

 large area with about forty grooves ; the margin crenulate, 

 and the grooves apparent on the inner surface, which is bluish- 

 white and pearly. When young, the valves are thin, and semi- 

 transparent, the epidermis yellowish-grey, or greyish-green, or 

 brown ; but ultimately they become thick and opaque, and the 

 epidermis black. 



A young individual, from deep water, off Aberdeen, was 

 shewn to me, in March, 1842, by Mr. Alexander Martin, one 

 of my pupils ; a large valve found by Mr. Davidson, in De- 

 cember, 1842. 



On the 26th December, 1842, when on an excursion with 

 my class, I found a great number of individuals in tufts of 

 Corallina officinalis growing in pools, at the Cove, four miles 



