Dr. J. E. Gray on the genera Furcella^ Teredo and Chsena. 297 



that, though the genus had two of the characteristics of the family 

 of Teredinidce, it wanted one of them ; the plates within were 

 only the palettes, which are simple and somewhat like those of the 

 more common Teredo norvegica ; there were no proper shelly valves, 

 not even any rudiments of them ; and that the animal forms a genus 

 in that family which has the abnormality of wanting the true shelly 

 valves so universal in the Conchifera. 



This absence may be explained by the fact that the animal does 

 not require them to protect its head and nervous centre, living as it 

 does in a soft sandy mud ; while they are required in Teredo and 

 the allied genera which have to bore their way into hard wood or 

 stone to form the hole that is to be lined with the shelly tube. 



Sir Everard Home in his * Lectures,' when describing the animal of 

 Teredo navalis (ii. t. 81), refers this shell-tube to the genus Teredo, 

 and gives a very good figure of the palettes, or as he called them, 

 "operculum," of it (tab. 81. f . 4 & 5) ; but he was not aware of 

 this absence of the shelly valve, for he figures what he considers 

 the '* boring shell of the same Teredo " (fig. 6) : but what he has 

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

 evidently a fragment of the plates which close the end of the 

 tube. 



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

 and have fallen out ; but I think this is impossible, as the holes at the 

 narrow part of the tube are very small, and filled up with fragments 

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

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

 were abundance of their pupa-skins in the cavity. 



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

 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 Conchifera 

 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, and probably from the same place, but with- 

 out 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 as in 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. 



