259 



of the tubes of the allied genera CUmagella and dapergittum\ and 



as these genera have the shelly valves of the animal in their proper 

 situations, on the sides of the body, quite distinct from the convex 

 caps, I think it is conclusive that they are not the hotnoloffue of the 

 valves, in those genera, as both the valves and the caps which are 

 considered as their homologue are present together, so tbat I must 

 consider the convex cap in those genera as 1 do in Fttrcella, as only 

 a continuation of the shelly tube in which the animal lives, and 

 having no more affinity with the shelly valves than the tube of G(U- 

 troiluena and some Idthodomi and other perforating Mollusca. 



Thirdly. It is to be remembered that some species of the true 

 genus Teredo, which have distinct shelly valves, also form a shelly 

 convex cap at the base of their tube in front of the animal, exactly 

 similar in structure and situation to the cap of the genus Furcella, 

 as I mentioned in my former paper ; so that I cannot consider it only 

 as a septum formed by the animal for its protection during the period 

 of rest in those species of Teredinidce which have true, well-deve- 

 loped, shelly valves, and the same convex caps as the homologue of 

 the shelly valve in the genus of the family which are without true 

 valves. 



Hence I must continue to regard Furcella as a Conchifer with- 

 out shelly valves or any part homologous to them ; and if we were 

 to find a Conchifer without valves, I should consider their absence 

 would be most likely to occur in a family which have the valves 

 in the normal members of it so reduced in comparison with the size 

 of the animal as in Teredinidce, where they have been regarded as 

 ** mere appendages of the foot ;" and also being a family of Bivalve 

 Mollusca, in which the animals always live in a shelly tube, it is one 

 in which the valves are least required for their protection. 



Since I sent in the former paper, I have had the opportunity of 

 examining Mr. Cuming's series of Furcella from the Island of Ca- 

 miguen, one of the Philippines, where they live in hard mud left 

 exposed at very low water. 



Mr. Cuming has several specimens of the tube of the young ani- 

 mal, which commence with a much smaller diameter than the spe- 

 cimen figured, and enlarge more rapidly in thickness, so that the 

 tube is more conical. He has two examples of the base of the tube 

 of larger specimens, which end in the cap formed of two overlap- 

 ping arched plates, like the one figured, showing that to be the 

 normal formation of the termination. All the specimens have two 

 separate apical siphonal tubes 



He has also two specimens of the upper part of the tube, which 

 are of a slender, elongated, nearly cylindrical form ; both are pierced 

 the whole length with two central semicvliudrical tubes, separated 

 by a narrow opake septum. One of these specimens i- water-wm n, 

 the other as fresh as if it had been broken from a living Bpecimen ; 

 the latter shows at the fracture that the apex of the tube is formed 

 of a Dumber of concentric laminae deposited one within the other. 

 The two semicylindrical siphon tubes are Burrounded with a special 



