274 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 58. Rhodophysa, 1 Blainville, 1834. 

 Rhodophysa, Blainville, Actinologie, p. 123 (sensu mutato). 



Definition. — Anthophysidse with a rudimentary nectosac at the distal end of the 

 bracts. Cnidonodes of the tentacles simple, without involucre, with a naked cnidoband 

 and a single terminal filament. 



The genus Rhodophysa was constituted by Blainville (24) for the reception of the 

 same three forms of Physonectse which Eschscholtz had united five years before in his 

 genus Athorybia. This latter name therefore has the right of priority. Retaining here 

 the name Rhodophysa, I employ it for those interesting, hitherto undescribed, forms of 

 Athorybidse, which differ from the others in the possession of a small rudimentary nectosac 

 at the distal end of the bracts. This structure is the same as is found in Athoria amon^ 

 the monogastric Athoridse (p. 201, PL XXI. figs. 5-10), and in the similar Athorula- 

 larvse of some Physonectse (p. 200). It is of great morphological interest, as a proof 

 that the bracts in this case are reduced nectophores. 



A single specimen of Rhodophysa was observed by me in the Indian Ocean during 

 my voyage from Ceylon to Aden (between the Maldive Islands and Socotra) in March 

 1882. It was in general very similar to the well-known Mediterranean Athorybia rosacea, 

 being also of the same light rose-colour, but differed in two essential points. Each bract 

 exhibited at the distal end a small rudiment of a nectosac, similar to that of Athoria 

 larvalis (PL XXI. figs. 5-10). Further, the tentilla possessed a naked spiral cnidotsenia, 

 with a single terminal filament, similar to the tentilla of Athoria and Forskalia 

 (PL X. fig. 23). Unfortunately the single specimen of this remarkable Rhodophysa 

 corona was destroyed before I could make a representation of it. It requires further 

 examination. 



Genus 59. Melophysa, 2 Haeckel, 1888. 

 Melophysa, Hkl., System der Siphonophoren, p. 42. 



Definition. — Anthophysidse with simple bracts, without nectosac. Cnidonodes of the 

 tentacles simple, with an involucre and a single terminal filament. 



The genus Melophysa comprises those Anthophysidse which have the general structure 

 of the typical Athorybia, but differ from it in the singular form of the tentilla, or the 

 cnidal knobs of the tentacles. Each tentillum bears a simple spiral cnidotsenia, the basal 

 half of which is enveloped by an involucre, and at its distal end a simple terminal 

 filament ; it is therefore similar to the tentilla of Stephanomia (9, pi. vi. fig. 8). 

 Respecting this difference, Melophysa exhibits a relation to Athorybia similar to 

 that which Stephanomia bears to Crystallodes, or Halistemma to Agalmopsis. 



1 Rhodophysa = Rose-bladder, polo*, q>vou. 2 Md )physa = Melon -vesicle, fifaov, quax. 



