244 



of the tube is solid and furnished with two separate tubular aper- 

 tures, evidently for the siphons of the animal, which in some speci- 

 mens are said to be produced beyond the end of the larger tube 

 into two slender, elongated, cylindrical tubules, as figured by Rum- 

 phius ; hence the name given to it by Oken : but I have never 

 seen a specimen which exhibited this character. 



The habit of the animal at once separates it from Teredo, which 

 always lives in wood, while the Furcella lives sunk perpendicularly 

 in the sandy mud of the tropical seas. 



The external appearance of the shelly tube agrees with this ha- 

 bitat ; for instead of being nearly cylindrical and more or less twisted 

 according to the hardness or knots in the wood, it is club-shaped 

 and closed at the larger end with a convex plate like the tube of 

 Chce?ia mumia, which lives in the sand in a similar manner ; but 

 the tube of the Furcella is much larger, and generally rather distorted 

 and irregular on the surface, divided into sections by more or less 

 distinct constriction of its diameter or by the slight alteration in the 

 direction of the tube, marked a, b, c, on the Plate, which on exami- 

 nation are evidently produced by the periodical stoppages in the 

 growth of the animal, which at each period of suspended activity 

 evidently closes up the end of the tube ; the animal absorbs this 

 terminal plate when it again returns to activity, and requires a 

 larger tube for its increasing dimensions. In the specimen before me, 

 the space between these interruptions in growth increased in length 

 as the animal grew and enlarged in diameter. 



The tube is thickened above as the animal leaves it, and is much 

 thinner near the lower or closed extremity. The whole length of 

 the tube is solid, without any perforations, except quite near the 

 closed end, where it is pierced with a number of unequal-sized rather 

 irregularly disposed small perforations, generally scattered ; but some- 

 times there is a short series of five or six placed in a longitudinal 

 line, and these holes appear to be filled up by an internal coat when 

 the animal absorbs the end and lengthens its tube. 



The larger end of the tube is entirely closed over by two convex, 

 arched, shelly laminae, continuous from each side of the tube, and 

 meeting and slightly overlapping one another in the central line, 

 which is opposite to the septum between the two tubes in the smaller 

 end of the shell-sheath of the animal. 



These small holes are evidently intended for admission of water 

 to the animal, and the shelly septa at the bottom to protect the 

 animal from the sand in which it lives. The holes are similar to the 

 tubes of Penicillus aquarius and Clavagella, which live in sand, 

 and Bryopa melitensis, which lives in porous stone. 



I have not observed any similar perforations in the tube of the 

 Teredo ; and indeed they would not be of any use, as the tube is 

 deeply sunk in the substance of the wood in which they burrow. 



The Teredines appear during their period of rest to close the end 

 of their tube, with a shelly septum formed of a single convex plate. 

 There are two fragments of tubes in the British Museum which ap- 

 pear to belong to that genus, from their external appearance and 



