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



can be distinguished. The distal mouth is often expanded in the form of a large circular 

 suctorial disc. 



Tentacles (figs. 1, 2, 5, t). — The long and very expansible tentacle which arises from 

 the base of each siphon (on its upper or dorsal side) is a cylindrical tube of rose-colour. 

 purple at the distal end, beset with a series of very numerous simple lateral branches ; 

 their length increases gradually from the proximal to the distal end. These tentilla are 

 thin cylindrical filaments with a simple rounded distal apex. Their canal is excentric, 

 since the thickened dorsal wall is filled with spherical cnidocysts (figs, 6, kc, 7), whilst from 

 the thinner ventral wall arise numerous conical papillae, each of which bears a palpocil or 

 a feeling bristle (fig. G, tw). 



Gonodendra. — The single gonodendron, which hangs down like a pediculate cluster 

 of grapes from each intern ode, midway between each two siphons, is rose-coloured and 

 composed of numerous secondary and tertiary gonodendra. Each of the latter (fig. 8) is 

 composed of a single large medusiform gynophore (f) and a corona of five to ten (usually 

 seven or eight) ovate androphores (h) around its base ; the distal end is occupied by a 

 large, very movable, spindle-shaped palpon (gq). Each branch of the gonostyle bears 

 two or three pairs of opposite secondary branches. 



Genus 70. Pneumophysa, 1 Haeckel, 1888. 

 Pneumoph ysa, Hkl., System der Siphonophoren, p. 45. 



Definition. — Rkizophysidae with loose cormidia, the gonostyles being attached 

 to the internodes of the stem, between the siphons. Tentacles branched; tentilla trifid, 

 with three terminal branches. 



The genus Pneumophysa differs from the preceding Nectophysa in the form of the 

 tentilla, which are not simple tubular filaments, but provided with three terminal 

 appendages similar to those of Cannophysa (PI. XXIV. figs. 8, 9). The odd median 

 appendage is larger and ampullaceous, whilst the two paired lateral horns are smaller and 

 slender. The cormidia are not ordinate, as in Cannophysa, but loose, so that a single 

 gonodendron is attached to each internode of the stem midway between two siphons 

 (almost as in Nectophysa, PI. XXIII. figs. 1-3). The single known species of this 

 genus, Pneumophysa gegenhauri, was observed by me in December 1881 in the Indian 

 Ocean, and will be described on another occasion. A second species, similar to this, 

 was noticed in my System der Siphonophoren (95. p. 45) as Pneumophysa mertensii 

 ( = Epibulia mertensii, Brandt, 25, p. 33). But a closer examination of the excellent 

 figures which its discoverer, Mertens, has left of this species, taken in the Tropical 

 Pacific, has convinced me that it belongs to the following genus, Rhizophysa. 



1 Pueumo j phijsa = Air-bladder, Tniiipa., (pvect. 



