424 COLLECTIONS FROM MELANESIA. 



Brit. Spong. iii. p. 204, pi. lxxiii. fig. 15); Vosmaer notes this 

 discrepancy. 



The British form of Gellius couchi has external characters similar 

 to those of Halichondria elegantia, and differs from it but slightly in 

 the spiculation. In the present collection occurs a specimen with 

 very similar spiculation, but the acerate is thinner and the fibre is 

 very distinct, the spicules being united by a yellow substance which 

 appears beyond the spicules on each side of the fibre. It has grown 

 over a Sertularian Hydroid, to which circumstance it probably owes 

 its elongate cylindrical form (that of 0. couchi is usually massive, 

 compact, and the spiculo-fibre is loose). The vents are scattered on 

 the surface, and measure only about 2 millim. in diameter. It may be 

 distinguished as var. ceratina. The following table gives the pro- 

 portions of the spicules in the type specimens of each of the three 

 forms here united : — 



Acerate. Bibamate. 



millim. millim. 



Hal. couchi, Bowerbank . . -24 by -Oil -02 by "0016 



Hal. elegantia, id -2 by -01 -025 by -016 



G. couchi, var. ceratina. . . . -23 by -0063-0079 "025 by -001 G 



Hah. Arafura Sea, 32-30 fms. 



Distribution. Straits of Malacca {Bowerbank)', Cornwall (Bower- 

 bank). 



59. Gellius varius. 



Halichondria varia, Bowerbank, P. Z. S. 1875, p. 292. 

 Isodictya virgata, id. I. c. p. 294. 



The above two species must be united. The erect cylindrical form 

 of well-grown specimens forms a good external distinctive specific 

 character, while the superior diameter (see below) of the skeletou- 

 spicule readily distinguishes it under the microscope. Two frag- 

 ments, exhibiting a cylindrical erect habit, occur ; the skeleton-fibre 

 is rigid and brittle, even in spirit-specimens, and agrees sufficiently 

 with that of the typical specimens ; the proportions of the spicules 

 are as follows : — 



Acerate. Bihamate. 



millim. millim. 



Hal. varia (type) -22 by '016 -025 to -032 by -0016 



Isodictya virgata (type) .. '22 by -014 -025 by -0021* 

 G. varia (from Pt. Darwin) -25 by -015 -019 by 0015 



Hah. Port Darwin, 8-12 fms. 



Distribution. Straits of Malacca (Bowerbank). 



60. Gellius fibulatus. 



Reniera fibulata, Schmidt. Adr. Meer. (l8(\2), p. 73 ; Atl. Geb. (1870), 



p. 40. 

 ? Isodictva jugosa, Bowerbank, Mon. Brit. Spunq. ii. p. 2'.»('., iii. pi. 2. 



figs. 11-1*4. 



