100 Memoirs of the Indian Museum. [Voi,. II, 



species or of D. neptuni from the genus Dichelaspis. D. neptuni is closely related to 

 D. sinuata, of which it may be a local racé or even a chance variety. 



■ Hoek, in his recent account of the Pedunculate Cirripedes of the " Siboga," 

 divides the genus into seven sections, much on the same principles as those adopted 

 in my key, which will serve to distinguish the Indian species not only from one 

 •another but from most other forms. There are, however, a few points that I have 

 been obliged to leave in doubt when preparing it. They may be noted here. I put 

 them in the form of questions as follows : — 



(i) Is D. sinuata merely a local race of D. lowei, Darwin ? Except as regards 

 size (which is not a reliable specific character in the genus owing to the 

 fact that few individuals reach the maximum dimensions they appear to 

 be capable of attaining) the difference between these two forms lies 

 mainly in outline, and this is not only a variable character in the softer 

 Lepadidse, but also one liable to be altered by bad or prolonged preserva- 

 tion. 



(2) Is D. sinuata distinct from the Japanese D. aymonini, I^esson ? So far as 



external characters go, I have examined intermediate specimens. 



(3) Is D. midier i, Coker, distinct from D. lowei ? The two are certainly very 



similar, but I have not seen either. 



(4) Are Stebbing's D. hoeki and D. antiquœ distinct from one another? The 



external differences between them are certainly smaller than those which 

 separate the extreme forms of D. tridens, a species belonging to the same 

 section of the genus. 



The following table shows the geographical distribution, bathymetrical range and 

 hosts of the Indian species of Dichelaspis , so far as these elements in their biology 

 have been ascertained. It will be noted that all the species are parasitic, or at least 

 commensal, in habits, but that the degree to which they are so varies considerably, 

 some attaching themselves to the exterior of their host, others penetrating within its 

 gill-chamber. 



An examination of the table shows that, with one exception, the Indian representa- 

 tives of the genus habitually affix themselves on settling down in life to the body of 

 some hard-shelled crustacean. The one exception is D. grayU which, so far, has always 

 been found on the skin of sea-snakes. As regards the species of Dichelaspis commonly 

 found on Crustacea it will be seen that at least two have been found occasionally on the 

 shells of echinoids, and that one (Z>. warwickii) sometimes fixes itself to the shells of 

 living molluscs, to the skin of sea-snakes and even to that of fish. As regards the crus- 

 tacean hosts of the genus, there is abundant evidence that the majority of the bar- 

 nacles prefer a hard-shelled decapod but are not particular as to its family. Decapods 

 are of course by far the commonest crustaceans of a considerable size and with hard 

 shells ; it is noteworthy that I have not found a single barnacle of any genus attached 

 to the carapace, limbs or gills of any of the soft-shelled prawns dredged by the '' Investi- 

 gator " or purchased in the Indian markets. Probably these decapods cast their skin 



