88 PHOLADID.'E. 



is more or less deeply incurved in the middle, and has, in 

 consequence, its lateral terminations more or less strongly 

 forked. The basal articulation is often peculiarly graceful 

 in shape, the lateral outline being formed by two convex 

 lines of corresponding curve on either side. The number of 

 these joints may average about a dozen, some apparently 

 having only eight distinct ones, whilst others (chiefly the 

 larger) have nearly twice that number. The articu- 

 lated 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 be- 

 yond the narrow bases, so as to cause the lateral edges to 

 appear serrated ; in certain specimens where the joints are 

 peculiarly distant, and their subtrigonal forms have become 

 in consequence less distinct, these forked terminations are 

 produced in narrow filaments, and the central concavities 

 are clothed with a more or less fringed membrane, which in 

 some measure conceals the depth of incurvation. So various 

 then are the aspects of both the pallets and the valves of 

 this interesting Teredo, that nothing but the long suite of 

 specimens in various stages of growth Avhich we have had 

 the good fortune to inspect and mutually compare, could 

 have enabled us to detect their specific identity. None of 

 the valves we have hitherto seen at all equal the dimensions 

 of our three first species, and the longest pallet was under 

 two inches in length. Those which have been delineated 

 in our plates, are very young, and are some of a large num- 

 ber extracted by Mr. Thompson, in Ireland, from the tim- 

 bers of a vessel returned from a foreign voyage. Some finer 

 ones are in Mr. Jeffrey's collection, taken by Mr. Clark, at 



