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



Each of these four species represents a distinct section of the genus, and there 

 can be no difficulty in separating one from the other. Bach, however, is represented 

 (with the exception of P. eburneum) in other parts of the Indo-Pacific region by 

 closely allied or racial forms, which must be separated, if they are really distinct, with 

 the greatest care. On the whole I think it best to regard P. eburneum as the type 

 of a distinct subgenus, for which the name Trilasmis, Hinds, is available. 



Pœcilasma kœmpferi, P. fissum and P. eburneum all appear to have an extensive 

 distribution. This is especially the case as regards the first, which occurs (either in 

 the typical form or so modified as to constitute a local race) on both sides of the 

 Atlantic, off the coast of Japan in the S. Pacific and in the Malay Archipelago, as well 

 as in the Gulf of Manaar. P. fissum was originally described from the Philippines 

 and has since been recorded from the Malay Archipelago and from several localities 

 in the S. Pacific ; while P. eburneum was first discovered at New Guinea and has since 

 been found in other parts of the Malay Archipelago and in the Persian Gulf and 

 the Red Sea. The original locality of P. minutum was Singapore ; I have examined 

 many specimens from the Bay of Bengal and the Arabian Sea. 



The different species differ considerably as regards their bathymétrie range. 

 P. kœmpferi is a deep-sea form, probably to be found only below the lOO-fathom line. 

 P. fissum and P. eburneum, on the other hand, belong to the littoral fauna. P. minu- 

 tum is abundant in the Arabian Sea at a depth of between lOO and 200 fathoms. 



Several species of Pœcilasma show a preference for Echinoids, to the spines of 

 which they are commonly found attached. This is the case as regards P. eburneum. 

 I have noticed that all the specimens I have examined have been fixed to the spines 

 on the oral surface of the host, in which position it is probable that stray fragments 

 of the Echinoid's food are more easily obtained by the barnacle than if it were 

 attached to spines on the anal or lateral surface. 



P. kœmpferi and its local races are usually attached to the carapace of spiny 

 crabs, but have also been found on sea-urchins ; while P. minutum apparently adheres 

 to any crustacean which it meets at the critical stage of its development. I have 

 found it most commonly on the carapace of Panulirus angulatus, but have taken two 

 Specimens on the capitulum of Pœcilasma kœmpferi. I have also found specimens on 

 the carapace and even in the gill-chambers — but there rarely — of several crabs. 



The following table gives a statement of the distribution, etc., of the Indian 

 species of the genus. I have dealt with these points in greater detail as regards the 

 species of the genus Dichelaspis, as I have more information about them than I 

 possess as regards those of the present genus. As a matter of convenience the two 

 Indian species of Megalasma are included in the same table — a position which the 

 similarity in structure and habits between the two genera abundantly justifies. 



