JOUSSEAUMIA. 263 



ganglia in the young forms, the simplicity of the alimentary tract (but this may be 

 due to degeneration), and such minor characters as the persistence of the internal 

 embryonic hinge ligament, the single pallial suture, &c. On the other hand, the 

 extensive fusion of the kidney-sacs in the middle line is characteristic of more highly 

 specialised Enlamellibranchs, such as the Anatinacea, and the presence of vesiculse 

 seminales is a unique feature of specialisation in connection with the reproductive 

 apparatus. 



Taking all these facts into consideration, we must regard Jousseaumia as an 

 offshoot of a primitive Eulamellibranch stock, which in consequence of its commensal 

 habits has been largely modified in the directions indicated, and that its nearest allies 

 are the Erycinidse and Galeommidae, which are similarly primitive Eulamellibranchs 

 modified in various directions in relation to their different habits of life. 



It is interesting to note that the commensalism between a coral, a sipunculid, and 

 a lamellibranch must be still further extended. In almost every specimen examined, 

 whether of Heterocyathus or Heteropsammia, I found in the Aspidosiplwn chamber 

 one or two specimens of a small copepod belonging to the family Harpacticidse, but as 

 I am obliged to bring this paper to a close to be in time for the issue of the last 

 volume of the " Reports on the Ceylon Pearl Oyster Fisheries," I have not had time 

 to identify the genus and species. Furthermore, Jousseaumia, minute as it is, and 

 protected within the AspidosipJioii chamber of the coral, is liable to the attacks of 

 parasites. In one series of sections I found a minute trematode, distinguishable as 

 such by its well-developed suckers, encysted in one of the dorsal lobes of the liver, 

 and in another series a larger specimen of what is apparently a trematode, but I could 

 not easily determine its nature from the sections, lying free in the supra-branchial 

 cavity. 



