478 PROCEEDINGS OF THE ACADEMY OF 



X. fimbria t a, Jeffreys. 



X. f imbr iata, Jeffreys, Ann. and Mag. Nat. Hist. 3d. ser. vi. p. 126. 



X. palmulata,* Forbes and Hanley, British Mollusca, i. p. 86, t. 2, f. 9-11. 

 Stimpson, Check-List, No. 249. Sowerby, Illust. of Brit. Shells, 1. 1. f. 6. 



T. bipalmulata, Thompson, Ann. and Mag. Nat. Hist., 1847. 



Hah. A doubtful inhabitant of the British coast. 



Description. The shell of this species differs so little from that of T. n a v a- 

 1 i s, that it is difficult to find any important distinctive characters in the valves 

 alone. They appear, however, to be always much smaller than in navalis, 

 and the external surface is not so highly polished ; the overlapping ledge 

 which internally marks the line of the posterior auricle is more elevated. 

 The valves inch in length. " The pallets, which are extremely fragile, 

 and never attain to any considerable dimensions, closely resemble diminutive 

 specimens of those ofbipennata. They vary much with age and circum- 

 stances in regard to the number of articulations, their closeness or laxity of 

 approach to each other, and even in their individual shapes. In the smaller 

 specimens, (and almost all hitherto taken in our seas belong to this class, not 

 exceeding half an inch in length, ) the stem resembles a piece of fine thread, 

 and is about equally long with the broader pennated portion which sur- 

 mounts it. This latter is composed of numerous somewhat triangular pieces, 

 of which the narrower end is jointed as it were to the broader opposite ex- 

 tremity of the preceding one, which is more or less deeply incurved in the 

 middle, and has, inconsequence, its lateral terminations more or less strongly 

 forked. The basal articulation is often peculiarly graceful in shape, the lat- 

 eral outline being formed by two convex lines of corresponding curve on either 

 side. The number of these joints may average about a dozen, some appa- 

 rently having only eight distinct ones, whilst others, (chiefly the larger) have 

 nearly twice that number. The articulated portion is usually about three 

 times* as broad as the stalk, and tapers towards its termination, where the 

 joints likewise are smaller and more closely set. In the larger pallets, where 

 the articulations are more remote from each other, their forked extremities, 

 instead of embracing (as in the young) the succeeding joint, project on either 

 side beyond the narrow bases, so as to cause the lateral edges to appear ser- 

 rated ; in certain specimens, where the joints are peculiarly distant, and their 

 subtrigonal forms have become in consequence less distinct, these forked ter- 

 minations are produced in narrow filaments, and the central concavities are 

 clothed with a more or less fringed membrane, which in some measure con- 

 ceals the depth of incurvation. . . None of the valves we have seen at all equal 

 the dimensions of our three first species, (Norvagica, marina, malleo- 

 lus,) and the longest pallet was under two inches in length. 



The tube was concamerated in Mr. Clark's examples (Exmouth) in the 

 cabinet of Mr. Jeffrey ; we confess, however, we perceived no indication of 

 such structure in the very small perforations of the Irish specimens ; in 

 both, the testaceous matter was sparingly deposited." Hanley. 



X. minima, Blainville, sp. 



T. minima, Blainville, Diet, des Sc. Nat. lii. p. 2GS. Fischer, Journ. 

 Conchyl. 2d ser. i. p. 256. Jeffreys, Ann. and Mag. Nat. Hist. 3d ser. 

 vi. p. 127. 

 T. lipalmulata, Delle Chiaje, Mem. iv. p. 28, t. 54, f. 18, 22. 23, 24. 

 T. palmulala, Philippi, Enum. Moll. Sicil. i. p. 3, ii. p. 2, t. 1, i. 8. 

 T. serratus, Deshayes, Mss. 

 T. Philippii, Gray, Ann. and Mag. Nat. Hist. 2d ser. viii. p. 386. Fischer, 



Journ. Conchyl. 2d ser. i. p. 257. 

 X. Philippii, Adams, Genera, ii. p. 333. 



* This is not the T. palmulataof Lamarck or Philippi. 



[Sept. 



