238 MALACOZOA. TROFIOl'OPA. LAMBLLIBHANCHIATA. 



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. Turk Brit. Biv. 199. 

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

 Mont. Test. Brit. 161. Modiola vulgaris. Flern. Brit. Anim. 412. 

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

 barbata. Lamk. Syst. vi. 1 14; Ed. 2. vii. 22. Mytilus Modiolus. 

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

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

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

 iv. 238. PL 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 arid 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 officmalia growing in pools, at the Cove, four milef 



