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convinced me that the darkest and hardest individuals are usually those which are 
attached to crabs or lobsters from the bottom, but there are exceptions to this rule. 
D. sinuata and D. angulata appear to be exclusively internal commensals. Their valves 
are more degenerate than those of any other species and their membrane is as a rule 
quite transparent. D. cor, which is usually less transparent and has rather less 
degenerate valves, is most often an internal commensal also ; but in one instance 
I found large numbers of this species attached to the posterior limbs as well as the gills 
of a crab. D. bathynomi is technically an external species, but the pleopods of 
Bathynomus are well protected by the shell which overhangs them, so that the barnacles 
have, so to speak, a roof over their heads. I have, however, also found a few examples 
of the barnacle attached to the extremity of the uropods, a much more exposed 
situation, and although D. bathynomus exhibits considerable variation as regards the 
extent of its valves, I have not been able to detect any difference in this respect 
between the individuals attached to the uropods and tho.se fixed to the pleopods. 
D. tridens, a form allied to D. bathynomi and like it belonging to the section of 
the genus in which the valves are least degenerate, is found most commonly on the 
mouth parts of its host or round the external margin of the entrance to the gill- 
chamber. It also occurs not uncommonly on the gills. All the external specimens of 
this species I have examined have had the valves more opaque than those of specimens 
from the gills ; but I cannot correlate the relative extent of the valves and membrane 
on the surface of the capitulum with any variation in habit. D. geryonophila is found 
both in the gill-chamber and at its external opening, clustering round the aperture 
at the base of the chelæ. 
It is not uncommon to find more than one species on the same host. For example, 
D. tridens and D. warwickii are frequently found together, while I have discovered 
D. angulata and D. sinuata on the gills of the same crab on more than one occasion. 
As regards the geographical distribution of the Indian species of Dichelaspis 
little of a definite nature can be said with confidence, for few specimens of most of 
them have as yet been reported by students of the Cirripedes in other countries. 
When the internal as well as the external characters of their decapod hosts are 
investigated, there can be little doubt that many specimens of the internal forms will 
be found to exist in museums. Almost every marine crab sold for food in the markets 
of Bengal harbours D. cor or D. angulata in its gill-chamber, and there is no reason to 
think that Bengali crabs are peculiar in this respect. Unfortunately, in these days 
of intense specialization, the student of the decapods frequently takes no interest in 
the Cirripedes. I cannot doubt that the majority of the representatives of the genus 
Dichelaspis obtained by the scientific expeditions that have visited tropical seas have 
never been recorded in their reports. 
However this may be, one point is clear as regards the Indian species, viz., 
that a large proportion of them have a considerable range in the northern part of 
the Indian Ocean, sometimes extending into the Pacific. D. warwickii, by far the 
most abundant shallow- water external form in the Bay of Bengal, extends from the 
Persian Gulf to the China Sea ; D. sinuata, a common species in the gill-chamber of 
