KEPORT ON THE SIPHONOPHORiE. 275 



During my residence in the Straits of Gibraltar, in March 1867, 1 once encountered a 

 small elegant Anthophysid, which at first glance I supposed to be a species of Athorybia. 

 A closer examination, however, demonstrated that the form of the tentilla was quite 

 different, each spiral cnidotaenia being half enveloped by a campanulate involucre and 

 ending with a single terminal filament (as in Anthemodes, PI. XV.). The form of 

 the bracts was very similar to that figured in Athorybia melo, which Quoy and Gaimard 

 had observed in the Strait of Gibraltar forty years before (2, pi. ii. figs. 7-12). It is 

 possible that these two forms are identical. The single specimen of Melophysa melo 

 captured was lost before I could make a drawing of it. 



Genus 60. Athorybia, 1 Eschscholtz, 1829. 

 Athorybia, Esch., System der Acalephen, p. 153. 



Definition. — Authophysidse with simple bracts, without nectosac. Cnidonodes of 

 the tentacles involucrate, trifid, with a median terminal vesicle and two lateral horns. 



The genus Athorybia, the oldest and best known form of Anthophysidse, was founded 

 by Eschscholtz for the reception of three closely allied species ; the typical Mediter- 

 ranean form described in 1775 by Forskal (11) as Physophora rosacea, and two species 

 observed in the Strait of Gibraltar by Quoy and Gaimard, and named Rhizophysa 

 heliantha and Rhizophysa melo (20). An accurate anatomical description of the 

 Mediterranean Athorybia rosacea was first given in 1853 by Kolliker (4, p. 24, Taf. vii.). 

 Athorybia heliantha from the Northern Atlantic seems to be closely allied to it; it 

 differs, however, in the special form of the tentilla described by Gegenbaur (10, p. 82, 

 Taf. xxxi. figs. 43, 44). ■ Another form of tentilla is exhibited in the Canarian 

 Athorybia ocellata described in the sequel, differing also from the former species 

 the form of the bracts and the possession of ocelli on the palpons. Another species, 

 distinguished by the form of the bracts as well as that of the cnidosacs, is Athorybia 

 indica, discovered by Huxley in the Indian Ocean and described under the name 

 Athorybia rosacea (9, p. 86, pi. ix.). The gonodendra of this species are monostylic, 

 while usually they are distylic. A number of different species of this genus seem to 

 inhabit all warmer seas ; they are, however, in general rare, and an accurate description 

 illustrated by figures taken from the living animals is required to render their com- 

 parison and specific distinction possible. Special attention must be paid to the bilateral 

 structure of the vesicular trunk, its ventral series of buds (PI. XII. fig. 9, ib, is), and the 

 relation of the nectostyle to the siphostyle. In some species of Athorybia the retracted 

 pneumatophore is covered on its ventral side by the prominent cucullate nectostyle, 

 as in Anthophysa (PI. XII. figs. 7-9). 



1 Athorybia = Pacific, aSotfific;. 



