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



Sciurella indivisa, n. sp. (PL V.). 



Trophosome. — Colony attaining a lieiglit of ten inches ; stem simple, monosiphonic, 

 sprino-ing in clusters from the hydrorhiza ; hydrocladia closely set, about two-tenths of 

 an inch in length, arranged in four longitudinal alternating series, which extend from the 

 summit of the stems to within a short distance of the base. Hydrothecse deep, nearly 

 cylindrical, adnate by their entire height to the supporting internode, every internode of 

 the hydrocladium carrying a hydrotheca, and having, in addition to the lateral nema- 

 tophores, a single mesial nematophore near its proximal end. 



Gonosome. — Gonangia in pairs from the axils of the hydrocladia, urn-shaped in front 

 view, with two symmetrically placed hollow lateral processes near the distal end; 

 gonangial nematophores carried by the lateral processes, by the summit of the gonangium, 

 and by its sides near the base. 



As already stated [see p. 22), I am not disposed to regard a scattered or multiserial 

 disposition of the hydrocladia as affording sufficient grounds for generic separation from 

 those forms of Antennularia in which the hydi'ocladia are verticillate. While, however, 

 the disposition of the hydrocladia in Sciurella indivisa would thus not in itself afford a 

 character by which this species could be generically separated from Antennidana, such 

 a character is found in the remarkable form of the gonangia, with their branching blasto- 

 style and the nematophores to which their walls give support. 



The general resemblance of Sciurella indivisa to Antenmdaria antennina is so close, 

 that, without the aid of a lens, a specimen of one of these hydroids might be easily 

 mistaken for the other. The gonangium, though urn-shaped when viewed in front, is 

 compressed laterally, and when viewed in profile is seen to have its axis curved backwards 

 nearly in a semicircle. 



The ramification of the blastostyle in the gonangium presents considerable symmetry, 

 and was similar in every instance examined. A strong branch is sent off on each side into 

 the lateral projections, and each of these branches sends out three short processes and one 

 long one, which all pass directly to the perforations in the walls of the gonangium, in order 

 to communicate with the corresponding nematophores which lie free on the outer surface of 

 the walls. The short processes pass to nematophores which lie near the distal end of the 

 gonangium, while the long processes pass down, one on each side, to communicate with 

 two nematophores situated near the base of the gonangium. 



The deep hydrothecae of Sciurella indivisa contrast with the small shallow hydro 

 thecse by which most species of Antennularia are characterised. 



Dredged off Somerset Island Cape York, Torres Strait ; 5-10 fathoms. 



