246 



here taken for the "boring shell," or true valves of the animal, is 

 evidently a fragment of the plates which closes the end of the tube. 



It may be supposed that, perhaps, the valves might be very small 

 and had fallen out ; but I think it is impossible, as the holes at the 

 narrow part of the tube are very small and scattered with fragments 

 of shell and sand. The tube otherwise is quite closed, and the 

 animal had evidently been eaten out by dipterous larva, as there 

 were abundance of the cases of their pupa-skins in the cavity. 



I may observe, that in the genus Penicillus, Brug. (Aspergillum, 

 Lamk.), which also lives in sand, and has a fringe of tubes round 

 the convex base of the tube, the shelly valves are immersed in the 

 substance of the tube ; but Furcella is the only genus of bivalve shells 

 I am acquainted with that is entirely destitute of true valves, like the 

 Tunicata. 



The possession of the two separate apertures at the upper extre- 

 mity of the tube does not appear to be exclusively confined to this 

 genus ; for in the British Museum we have three specimens of tubes 

 which belong to Teredo norvegicus, or to a species allied to it, pro- 

 cured at the same time probably from the same place, but without 

 any habitat. 



They all have a succession of transverse laminae at the upper extre- 

 mity of the tube. In No. 1 these plates are pierced with an oblong 

 central hole for the passage of the siphons, as is the case with most 

 specimens of T. norvegicus. No. 2 is similar, but there is a pro- 

 jection on one side of the perforation of the plates dividing the aper- 

 ture on that side into two parts ; and in No. 3, instead of having a 

 single oblong aperture as in the other specimens, there are two sub- 

 circular ones separated by a central transverse septum asm Furcella, 

 as if the imperfect rib in No. 2 was transformed into a shelly plate 

 extending right across the aperture, and which must be deposited 

 between the two siphons of the animal. 



In general the tubes of Teredo are entirely imbedded in the wood, 

 but sometimes, as in a specimen we have in the Museum from the 

 mouth of the River Nunn, the apices of the tubes of the shell pro- 

 ject as if they were produced by the animal as the shelly tube en 

 larged beneath ; but I believe this arises from, and at least is pro- 

 bably, if not entirely, produced from the surface of the wood disin- 

 tegrating and leaving the apices of the tubes exposed. In the same 

 collection are a series of the tubes of a species of Teredo, from 

 Van Diemen's Land, which are more or less covered with Serpulce 

 and Vermeti ; I suspect these must be specimens which have been 

 partially or entirely exposed by the rotting of the wood in which 

 they were enclosed. 



These specimens from Van Diemen's Land, so covered with Serpulce, 

 also exhibit another peculiarity : in one case two tubes are parallel 

 to each other, and firmly united by the outer surface of one of their 

 sides into one body, which induced me to believe that they might be 

 Serpulce, until I examined the structure of the shell and observed 

 the simple contracted apex of the upper extremity. 



In those genera of Teredinidce which have a number of half-septa 



