800 MR. J. RITCHIE ON HYDEOIDS [^f'lj 2-i, 



asterisks in the following list, have thus been added to the 

 fauna of the Indian Ocean. As to the wider relationships : — 

 Three species are peculiar to the Indian Ocean {Corydendrium. 

 sessile, Hehella crateroides, CalyceUa oligista), leaving twenty- 

 six to be accounted for. Of these, twelve are so widely 

 distributed that tlieir occui-rence, emphasizing the normal nature 

 of the fauna, can give no indication of special affinity : three 

 Ijeing found in the Atlantic and Xorth Pacific Oceans and in Aus- 

 tralasian seas (Opercidwell a lacerta, Plvjmdaria setacea, Anienella 

 secundaria) ; two in the Atlantic and North Pacific Oceans 

 {Ferigonimusrepens, Campanulariararidentaia) ; and seven in the 

 Atlantic Ocean and in Malay- Australian seas {Pennaria disticha, 

 Haleciuni tenellimi, Canipanularia corrugata, Hehella calcarata, 

 ^ertularella polyzonias, Idia pristis, Diphasia digitalis). Of the 

 remaining fourteen, four have been found only in the Atlantic 

 Ocean (Eiulendrium aUemiattim, Cuspidella costaia, Lafoea serraia, 

 Lafo'ea venusta), seven in the Malay- Australian area {Eudendrium 

 generalis, Cladocoryne haddoni, Halecitmi sitnplex, ThyroscypMm 

 vitiensis, Sertularella cylindrica, Sertularella quadrideiis, Sertularia 

 turbinata), one in the ISTorth Pacific Ocean ( Thyroscyphiis regularis), 

 and two in both the last-named areas {Lytocarpus ]3ennarius and 

 L. phoeniceus). 



The closer relationship is obviouslv with the fauna of the 

 Pacific Ocean (represented by ten distinctive species), and in 

 particular with the Malay-Australian portion of that ocean 

 (represented by seven species). The significance of the apparent 

 Atlantic affinity is minimised when it is understood that of 

 the four species common to it and the Mergui Archipelago, one 

 (Eudendrium attenuatum) is identified with much doubt, while 

 the remaining three are very minute epizoic species, the presence 

 of which in other regions may conceivabh' have been overlooked. 

 It is i-emarkable that of the thiity species recorded, seven- 

 teen were found climbing upon larger Hydroids and one upon 

 a Polyzoon, the majority being minute, habitual epizoa, be- 

 longing in the main to the families Halecidfe, C'ampanularidje, 

 Campanulinidse, and Lafoeidre. The examination of this collection, 

 and of others, leaves with me the di.stinct impression that the 

 epizoic Hydroids are not distributed indisciiminately ujion all 

 types of Hydroid host. Thus, in general, the members of the 

 family Plumularida; remain comparatively free from extraneous 

 gro\\-ths — a fact to be correlated, perliaps, with their possession 

 of nematophores ; while colonies, belonging especially to the 

 famUj' Sertularida;, are occasionally so overgrown that the 

 structures of the host are much obscured. Even distinct pre- 

 ferences for certain species may be observed. Taking, for each 

 epizoic species in this collection, the total numbers of stations at 

 which it was found, and adding those numbers for all the epizoic 

 species, we find that epizoic species were found at a sum total of 

 forty five stations. At thirty-tico of these Idia pt-istis was either 

 the only host, or one of the hosts where more than one species 

 L2J 



