MALACOZOA. TROPIOPODA. LAMELLIBEANCHIATA. 295 



umbo to the posterior-inferior margin ; the cardinal laminae 

 elliptical, concave, very thin, projecting vertically, and strength- 

 ened by an oblique fold and a narrow plait, running backwards 

 and downwards, with a glossy pearly space near the liinge ; 

 the colour white. The pearly space is more conspicuous in dead 

 shells, in which it retains its lustre, while the rest of the shell 

 has become dull. I have seen a pearl or pearly protuberance 

 formed in it. Length neai-ly an inch and a4ialf, height an inch. 



Frequently brought up by the fishing-lines, from deep water, 

 off Aberdeen. Found by me in December, 1841, afterwards 

 by Mr. Leslie, and in October, 1842, by Miss Marion Mac- 

 gillivray. 



Mja. prtetenuis. Penn. Brit. Zoo]. Ed. n. iv. 160. PI. 50. f. 1.— 

 Mya praetenuis. Mont. Test. Brit. 41. PI. 1. f. 2. — Anatina prae- 

 tenuis. Turt. Brit. Biv. 48. PI. 4. f. 4. — Amphidesraa prcetenue, 

 Flem. Brit. Anim. 432. 



2. Anatina trimcdta. Truncated Anatina. ' 

 Shell subovate, rather compressed, very thin, brittle, pellucid, 

 "with the anterior end much larger and rounded, the posterior 

 narrowed and subtruncate, the anterior dorsal outline little con- 

 vex, the posterior nearly straight ; concentrically rugoso- 

 striate ; the surface slightly glossy, very minutely punctulate, 

 at the posterior end roughish with minute prominences ; an 

 obscure ridge from the umbo to the posterior-inferior margin ; 

 the cardinal laminae oval, concave, thick, projecting vertically, 

 and strengthened by an oblique fold (but no narroAv plait) 

 nmning backwards near the margin, with a glossy pearly 

 space near the liinge ; the colour white. Length of an indi- 

 vidual an inch and a-twelfth, greatest height seven and a-half 

 twelfths. 



This species differs from Anatina praetenuis in being larger, 

 in having the anterior part higher, the posterior shorter, nar- 

 rower, and more truncate, the cardinal lamina much thicker, 

 without a narrow plait supporting it. 



First found by me in October, 1842, among shells and coral- 

 lines from deep water, off Aberdeen. 



Mya declivis. Mont. Test. Brit. PI. 1. f. 2. — Anatina declivis. 

 Turton, Brit. Biv. 47. — Amphidesma declive. Flem. Brit. Anim. 

 432. — Anatina truncata. Linn. Syst. Ed. 2. vi. 77. 



Genus 6. Thracia. 



Shell ovato-oblong, inequivalve, inequilateral, very 

 thin, brittle, rounded anteriorly, more or less truncate 



