476 PROCEEDINGS OP THE ACADEMY OF 



X. bipesxata, Turton. 



X. bipennata, Turton, Conch. Diet. p. 184, f. 3S 40. Turton, Conch, dith- 

 Brit. p. 15. Brown, Conch. Gt. Brit. p. 116. Catlow, Conch. Nomenc. 

 p. 2. Fischer, Journ. Conchyl. 2d ser. i. p. 257. Fleming, Brit. Anim. 

 p>. 454. Gray, Phil. Mag., 1827, p. 411. Hanley, Desc. Cat. p. 4, t. 9, 

 f. 50. Hanley, Brit. Mollusca, i. p. 80, t. 1, f. 9 11. Jeffreys, Ann. 

 and Mag. Nat. Hist. 3d ser. vi. p. 126. Quatrefages, Ann. des Sc. Nat. 

 3d ser. xi. p. 30. Thorpe, Brit. Mar. Conch, p. 28. 

 X. pennatifera, (part.) Gray, Ann. and Mag. Nat. Hist. 2d ser. viii. p. 386. 

 X. carinata, Leach, Adams, Genera, ii. p. 333. 



T. carinata, Leach, Blainville, Diet. Sc. Nat. lii. p. 269. Catlow, Conch. 

 Nomenc. p. 3. Gray, Ann. and Mag. Nat. Hist. 2d ser. viii. 

 p. 36S. 

 T. carinata, Blainville, Fischer, Journ. Conchyl. 2d ser. i. p. 256. 

 T. carinata, Gray, Phil. Mag., 1827, p. 411. Hanley, Desc. Cat. p. 4. 

 T. navalis, Home, Philos. Trans., 1806, p. 276. Home, Comparit. Anat. ii. 



t. 43. 

 Hah. England (bipennata), a doubtful native. Sumatra (carinata). 

 Coll. Acad. Nat. Sciences. 



Description. "Valves with the body or medial portion narrow and elong- 

 ated. Auricle tipically projecting higher than the beaks ; its upper internal 

 edge most strongly reflected outwards ; the lower internal edge scarcely slop- 

 ing, and projecting shelf-fashion over the body. Triangular area extending 

 as low down as the auricle, not large, its outer edge very oblique ; tooth-like 

 apophysis greatly slanting posteriorwards. Pallets very large, quill-shaped, 

 of a spongy texture. 



The shape of the valves is very different from that of Norvagica or 

 Batava, the medial portion being decidedly more elongated, and the lower 

 end of the auricle slightly more remote from the ventral tubercle than is that 

 of the front triangle. This latter occupies less than two-fifths of an imaginary 

 line drawn from the beaks to the base of the shell, and is concentrically tra- 

 versed by raised stria?, or narrow lyra?, which are moderately close-set, and 

 not much arcuated below, but more distant and more curved towards the com- 

 mencement of the series. These are succeeded by another set of minutely 

 decussated stria?, which occupy the narrow strip situated between the lateral 

 triangle and the internal radiating groove, and are produced thence along the 

 front margin of the shell. Then follows a still narrower strip, which, together 

 with the preceding, is elevated towards the beaks above the remainder of the 

 surface, covered with very oblique, distant, raised concentric stria?, often with 

 finer intermediate ones, which, after passing the central, shallow, groove-like, 

 radiating area, are more or less distinctly continued over the remainder of the 

 surface as far as the auricle. This latter, which is smooth, small, and ear- 

 shaped, projects at its upper part above the summit of the beak, and is inter- 

 nally cut off as it were from the body of the shell by its lower edge, which, 

 almost straight and scarcely declining, projects like a ledge over the subum- 

 bonal region. Its basal line is thus almost at right angles to the hinder mar- 

 gin, whilst its much arcuated posterior outline runs nearly parallel to the base 

 of the lateral triangle. This ear-shaped appendage is also most strongly 

 reflected outwards, and is internally rather closely grooved with concentric 

 costella? ; its hinder termination is attenuately rounded, and its front extrem- 

 ity is in the adult concavely, in the young subrectilinearly, more or less ob- 

 liquely subtruncated. 



The entire shell is white and faintly glossy ; there is an extremely oblique 

 lamina surmounted by a tooth-like process upon the hinge margin, running 

 at acute angles to the very oblique and flat subumbonal blade, which latter is 

 clavate, and in the most perfect specimens we have met with either tubercu- 



[Sept. 



