ACTINOGONIUM PUSILLUM. 273 



*^* AcTi\OGONiUM PUSILLUM, Vail Bcneilen. 



Syncoryne rusiLLA, — Van Beneden, Mem. sur rEmbryog. des Tubulaiics, p. 53, pi. iii, 



figs. 1—12. 

 CoRYNE Van Benede.vii, — Uincks, Brit. Ilydr. Zoopli., p. 15, pi. ix, fig. 1. 



TROPHOSOME.- — Hydrocaulus attaining a height of about one eighth of an 

 inch, capillary irregularly ramified; pekisarc thin, transparent, slightly annulated. 

 Htdbauths with about twelve tentacles. 



GONOSOME. — GoNOPHOBEs few in number, globular, on short peduncles borne by 

 the hydrauth at the base of the inferior tentacles. Actinulj^ mth four tentacles. 



Colour. — Perisarc pale-yellowish. 



Habitat. — Attached to the carapace of crabs and to various other bodies. 



Locality. — Coast of Belgium, M. Van Beneden.' 



The Syncorijne pusilla of Van Beneden is certainly not the Coryne pusilla of Gartner, though 

 the latter is cited by the Belgian zoologist under the synonymes. There is, moreover, some con- 

 fusion between the Syncoryne 2msilla of the ' Memoir on the Embryogeny of the Tubidarians' and 

 a liydroid to which Van Beneden refers this species in his later memoir (' Faune lit. dc Belgique'). 

 The species of the later memoir bears medusiform planoblasts, and woidd seem to be a true 

 Syncoryne, though no description of it is given sulficient for diagnosis. M. Van Beneden 

 declares that it would be difficult to say whether it differs really from the Syncoryne decipiens of 

 Dujardin. 



From the description and figures given by Van Beneden of the Actinoyonium jjiisillum it is 

 impossible to regard the body which has liberated itself from the sporosac as other than an 

 actinula. Van Beneden describes it as resembling a minute cuttle-fish with four arms (" poulpe a 

 quatre bras "), and he further compares it to the free planoblast described by M. de Quatrefages 

 under the name of Elentlieria. 



Through the kindness of IM. Van Beneden I have received specimens of his Syncoryne 

 pusilla preserved in spirits, but with the gonosome, unfortunately, in so imperfect a state as to 

 render it impossible to demonstrate in it the important points described by the distinguished 

 Belgian zoologist. Mr. Hincks, however, has been more fortvraate, for in specimens supplied 

 some time ago by jM. Van Beneden to j\lr. Alder, he has succeeded in confir-tning the pre- 

 sence of actinulffi. He has also detected in the walls of the sporosac four canals extending 

 from the base to the summit. 



The Actinoyonium pusillKm is thus one of the very few hydroids in which the development 



' Johnston (' Biit. Zoopli.,' pi. iv, figs. 1, 2) figures among British species a eoryuiform liydioid, 

 which he refers, though not without doubt, to the Syncoryne pusilla of Van Beneden. We have not 

 yet, however, evidence which can be accepted of the discovery of \a.\\ Beneden's hydroid on the 

 British shores. 



