102 Memoirs of the Indian Museum. [Vol. II, 



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. hathynomi 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 those fixed to the pleopods. 

 D. tridens, a form allied to D. hathynomi 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 chelae. 



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. Unfortunateh^, 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 



