MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 239 



south of Aberdeen. I have also minute specimens found in 

 shell sand from Crude n Bay, and Ugie-mouth. 



Mytilus discrepans. Mont. Test. Brit. 169; Suppl. 65. PI. 26. 

 f. 4. — Modiola discrepans. Turt. Brit. Biv. 202. — Modiola discre- 

 pans. Flem. Brit. Auim. 413. 



3. Modiola discors. Tumid Ribbed Modiole. 



Shell ovate, tumid, very thin, transparent ; with a yellowish- 

 grey epidermis, under which it is irregularly concentrically 

 banded with reddish ; umbones tumid, incurved ; anterior end 

 broader, the other obliquely angulate ; about sixteen fine 

 grooves from the umbo to the anterior margin ; toward the 

 middle a smoothish space ; a larger posterior area with about 

 fifty grooves ; the margins crenulate, and the grooves apparent 

 on the inner surface. Length eight-twelfths of an inch, height 

 five-twelfths. 



Common in the leathery envelope of Ascidiae ; frequently 

 brought up by the lines. 



Mytilus discors. Linu. Syst. Nat. i. 1159. — Mytilus discors areis 

 tribus distinctis. Walker, Test. Brit. 167. — Modiola discors. Turt. 

 Brit. Biv. 201. — Modiola discors. Flem. Brit. Anim. 413. — Modiola 

 discrepans. Laiuk. Syst. vi. 114; Ed. 2. vii. 23. 



Genus 3. Pinna. Fan-Mussel. 



Animal elongated, obovato-triangular. The lobes of 

 the mantle united on the dorsal margin, separated in 

 the rest of their extent, generally ciliated on the edges. 

 Mouth between two very elongated lips, terminated by 

 two pairs of short palpi. Foot slender, conical, vermi- 

 form, furnished at the base behind with a very copious 

 silky byssus. Abdominal mass moderate. On each 

 side a pair of nearly equal, semilunar branchiae. An- 

 terior adductor muscle small ; posterior rather large, 

 sub cylindrical, and nearly central. 



Shell elongated, obovato-triangular equivalve, ine- 

 quilateral, moderately convex, compressed behind, con- 

 centrically striated, often longitudinally costate, and 

 muricate, thin, horny, semitransparent, fragile. Um- 

 bones very small, terminal. Hinge toothless, with 

 transverse internal lamellae in the angle of the umbones. 

 Ligament very long, linear, in a very narrow, marginal 

 groove, subinternal, occupying more than half of the 



