Report on the zoological collections made in the Indo-Pacific Ocean ...

——424 COLLECTIONS FROM MELANESIA.Brit. Spong. iii. p. 204, pi. Ixxiii. fig. 15); Vosmaer notes thisdiscrepancy.The British form of Gellius couclii has external characters similarto those of Halicliondria elegantia, and differs from it but slightly inthe sjjiculation. In the present collection occurs a specimen withvery similar spiculation, but the acerate is thinner and the fibre isvery distinct, the spicules being united by a yellow substance whichappears beyond the spicules on each side of the fibre. It has grownover a Sertularian Hydroid, to which circumstance it probably owesits elongate cylindrical form (that of G. couclii is usually massive,compact, and the spiculo-fibre is loose). The vents are scattered onthe surface, and measure only about - millim. in diameter.It may bedistinguished as var. ceratina. The following table gives the proportionsof the spicules in the type specimens of each of the threeforms here united :Acerate.Bihamate.millim.millim.Hal. couchi, Bowerbank . . -24 by -Oil -02 by -0016Hal elegantia, id -2 by -01 -025 by -016G. couchi, var. ceratina. ... -23 by •0063--0079 '025 by -0016Hab. Arafura Sea, 32-36 fms.Distribution. Straits of Malacca {Bowerbank); Cornwall {Boiverhank).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 formof well-grown specimens forms a good external distinctive specificcharacter, while the superior diameter (see below) of the skeletonspiculereadily distinguishes it under the microscope. Two fragments,exhibiting a cylindrical erect habit, occur ; the skeleton-fibreis rigid and brittle, even in spirit-specimens, and agrees sufficientlywith that of the typical specimens ; the proportions of the spiculesare as follows :Acerate.Bihamate,millim.millim.Hal. varia (type) -22 by -016 -025 to -032 by -0016Isodictya virgata (type) . . -22 by -014 -025 by -^21G. varia (from Pt. Darwin) -25 by -015 -019 by 0015Hab. Port Darwin, 8-12 fms.Distribution.Straits of Malacca (Bowerbank).60, Gellius fibulatus.Reniera fibulata, Schnndt, Adr. Meer. (1862), p. 73 : Atl. Geh. (1870),p. 40.? Isodictya iugosa, Bowerbank, Mon. Brit. Spvny. ii. p. 206, iii. pi. 2.tigs. 11-14.