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

;428 COLLECTIONS FROM MELANESIA.somewhat too wide a scope, it is at the same time true that a restingplace or places must be found for those numerous and varied specieswhich are intermediate between the more plainly marked generaDesmacidon, Esperia, and MyxiUa. For some of these forms oldergenera may be employed, e.g. Dirrhopalum^Plocamia) for A. coriaceusand microcionides (as I have endeavoured to show in a paper " Onthe Genus Plocamia &c.," Journ. Linn. Soc, Zool. xv. pp. 481, 482).For some such species (ahyssi, pldnctenoides) Mr. Carter employsthe old term Jlaliehondria ; but the type of Fleming's genus Ha-Ikliondria is Sponc/ia papillaris^ Pallas, which appears to be asynonym of Halicliondria {Amorphina^ Schmidt) ^?a«?'o^rt, viz. aEenierid and not a Desmaeidine, and so the genus Halichondria, ifmaintained, should be restricted to Renieridse.AmpJiiJectus, it seems to me, may be kept with advantage forforms with dentate or navicular equianchorate flesh-spicules, withsmooth skeleton-spicules and absence of anv echinating spicules : thetype of the genus is Isodictya gracilis of Bowerbank. It may beperhaps necessary to admit forms in which the tibiella (when present)is slightly spined, as in Desmacidon anceps, Schmidt. Vosmaer'slimitation of Desmacidon to species with horny fibre is not justifiedby the species he has assigned to it.63. AmpMlectus tibiellifer. (Plate XLII. figs, t-t" .)Erect, massive, sessile by broad base ; sponge broader than highand higher than it is thick, decreasing in thickness towards uppermargin, which presents a narrow edge. Sponge-mass honeycombedby a system of tortuous, anastomosing spaces, 3 millim. and upwardsin diameter, separated in most cases merely by trabeculte of substance.Surface perforated by the closely-set openings of the abovementionedspaces ; surface of sponge and of the trabecuLie betweenopenings even, slightly villous in spirit. Texture of sponge inspirit firm, subelastic, tough ; colour dark reddish umber-brown.Sarcode pale reddish brown, rather soft. Main skeleton consistingof compact spiculo-fibre formed of spicule no. 1, sliowing nohorny uniting substance, about 3 to 6 spicules broad, irregularsome only of the primary fibres go straight to surface, the secondaryfibres usually meet the primaries at acute angles ;primariesabout "5 millim. apart. Dermal skeleton consisting of a networkof spiculo-fibre 2 to 4 spicules broad, the spicules mostly looselyaggregated ;meshes of network about '35 millim. apart.Spicules :—(1) Skeleton acuate, strong, smooth, straight or slightlycurved ; base rather squarely rounded, shaft cylindrical, taperingto point from about three diameters from end; size -38 by -014millim. (2) Tibiella, slender, almost straight ; shaft smooth, ofsame diameter throughout, passing gradually into an oval smoothhead about half as thick again as sh;ift; size -25 by -0042 millim.(thickness of head) : abundant in dermal membrane and interior.(3) Equianchorate, navicular or shuttle-shaped, with palms rather