130 THE VOYAGE OF H.M.S. CHALLENGES. 



its apex, where the top of the stem is inserted ; it is protected at its ventral side by the 

 two overlapping wings, and opens below by a dilated basal mouth, whence issues the 

 siphosome. 



Somatocyst (cs). — The uppermost rounded apical part of the nectophore is occupied 

 by an ovate somatocyst, which arises, as the apical prolongation of the stem, between 

 the apical ends of the nectosac and the hydrcecial canal. It is filled with large vacuolate 

 entoderm cells, and contains in its rounded apex a globular oleocyst (co). 



The somatocyst of the Indian Monophyes princeps is wanting in the Atlantic 

 Monophyes hydrorrhea, and the similar Mediterranean Monophyes diptera (Chun, 87, 

 Taf. ii. fig. 5). These two species represent an older phylogenetic state, since the two 

 parallel ventral wings of the nectophore are separated in its whole length, and not united 

 in the apical third ; this difference explains the absence of the somatocyst in them. 



Siphosome (figs. 13, 14, as). — The common stem, retracted into the hydrcecial canal 

 {id), was in the specimen observed rather short (probably broken off), and bore (besides 

 numerous small buds) not more than five or six immature eudoxomes. Each eudoxome 

 had a hemispherical bract and, protected by it, a siphon with its tentacle, and a small 

 ovate gonophore ; the form and structure of these parts, which I could not sufficiently 

 examine, seems to agree with those of Monophyes irregularis. 



Genus 19. Sphseronectes} Huxley, 1859. 

 Sjjhceronectes, Huxley, The Oceanic Hydrozoa, p. 50. 



Definition. — Monophyidae with a rounded, edgeless, subspherical nectophore, and a 

 complete tubular hydrcecium on its ventral side ; the latter includes the siphosome. 

 Bracts mitriform or subspherical, with rounded surface and a simple phyllocyst (Diplo- 

 physa, Genus 10). 



The genus Sphseronectes was founded in 1859 by Huxley for an Australian 

 Monophyid, Sphseronectes kbllikeri? which was remarkable for a single subspherical 

 nectophore with a tubular hydrcecium. Another closely allied Mediterranean species 

 was described fifteen years later by Claus under the name Monophyes gracilis (70, 

 p. 29, fig. 8). The same author there gave the description of a similar third Monophyid 

 under the name Monophyes irregularis (ibid., p. 32, figs. 16, 17). We retain the 

 generic name Monophyes for this latter species, whilst the two former are better 

 placed in Huxley's original genus, Sphseronectes. The first-described Australian species, 

 Sphseronectes Tcdlliheri, differs from the Mediterranean Sphseronectes gracilis in the 

 flatter, more depressed nectophore, and the subhorizontal, not geniculate somatocyst. 

 A specimen of Sphseronectes holliheri was found by me in the Challenger collection, 

 taken from the surface of the Tropical Pacific at Station 274. The same bottle con- 

 1 Sphseronectes = Swimming sphere {o<pou%u,, kijxtjis). 2 9, p. 50, pi. iii. fig. 4. 



