1909.] N. Annandale : The Indian Cirripedia Pedunculata. loi 
too frequently for them to be suitable hosts. Apart from soft-shelled forms, D. 
vaarwickii apparently affects any decapod from shallow water or the surface of the sea 
that it happens to meet at the critical moment in its existence at which the larva 
must become sedentary. It is equally common on crabs like Doclea ovis that hug the 
bottom, on crabs like Neptunus pelagicus that swim on the surface, and on lobsters 
such as Panulirus fasciahts. D. angulata, D. sinuata, and perhaps to a less extent 
D. cor , are also somewhat catholic in their tastes, but, so far as is known, only choose 
decapod hosts and are usually found on pelagic species. As they are almost invariably 
found in the gill-chamber of the crabs and lobsters they honour with their company, 
it is improbable that hosts without gill-chambers attract them. D. bathynomi , on the 
other hand, has only been found on the pleopods and uropods of the largest of known 
Isopods, viz., Bathynomus giganteus — a species with a hard shell and sometimes as 
much as ten inches long. D. rhinoceros and D. stella have each been taken on one 
occasion only. It is therefore impossible to say anything as regards their choice of 
hosts with confidence ; both were found in the gill-chambers of bottom-haunting deca- 
pods. The case of D. geryonophila is very remarkable. It is apparently not uncom- 
mon on the gills of a certain crab {Geryoii quinqnedens) frequently obtained from deep 
water off the coast of New Jersey in North America. A single individual of an allied 
crab (G. apfinis) has been obtained in Indian seas, representing a species originally cap- 
tured near the Azores. I have examined both this specimen and one of the American 
species ; round the entrance to the gill-chamber of both I found the barnacle in large 
numbers, the Indian examples agreeing so closely with the American ones that it is 
impossible even to regard them as representing a specialized local race. Dichelaspis 
geryonophila , up to the present time, has, therefore, only been taken with crabs of the 
genus Geryon, and with them only in the western part of the North Atlantic and in the 
Laccadive Sea. 
As regards the position on or in the body of their host assumed by barnacles of 
this genus, it is possible to divide them roughly into two categories, (i) those that 
attach themselves to the external surface and (2) those that penetrate into the gill- 
chamber. To some extent it may be said that the latter are more degenerate as re- 
gards their shell than the former. In both respects, however — that is to say, both as 
regards habit and as regards structure — there are intermediate stages. D. grayii 
belongs to the first category, but in its transparent integument and minute valves 
resembles those species which frequent the gill-chambers of crabs. D. grayii, however, 
is the most thoroughly pelagic species of the genus as yet known, and in many 
groups of the animal kingdom a pelagic life is associated with transparency and 
softness of the tissues ; Lepas tenuivalvata , in which the shape of the tergum and scu- 
tum, so far as it is ascertainable, remains typical of the genus Lepas, exemplifies this 
fact by the transparency and lack of calcium of its shell. D. warwickii is generally 
found on the external surface of its host, but on two occasions I have found small, 
colourless specimens of the species in the gill-chamber. Few species vary more than 
this one as regards the colour of the membrane of their capitulum and the degree to 
which their valves are calcified. The examination of hundreds of specimens has 
