_Dosilia_, J. E. Gray, P. Zool. Soc. London, 1867, p. 550. TYPE, _Spongilla plumosa_, Carter. This genus is distinguished from _Ephydatia_ by the nature of the free microscleres, the microscleres of the gemmule being similar in the two genera. The free microscleres consist as a rule of several or many shafts meeting together in several or many planes at a common centre, which is usually nodular. The free ends of these shafts often possess rudimentary rotulæ. Occasionally a free microsclere may be found that is a true monaxon and sometimes such spicules are more or less distinctly birotulate. The skeleton is also characteristic. It consists mainly of radiating fibres which bifurcate frequently in such a way that a bush-like structure is produced. Transverse fibres are very feebly developed and are invisible to the naked eye. Owing to the structure of the skeleton the sponge has a feathery appearance. Gray originally applied the name _Dosilia_ to this species and to _"Spongilla" baileyi_, Bowerbank. It is doubtful how far his generic description applies to the latter, which I have not seen; but although the position of _"Spongilla" baileyi_ need not be discussed here, I may say that I do not regard it as a congener of _Dosilia plumosa_, the free microscleres of which are of a nature rare but not unique in the family. With _Dosilia plumosa_ we must, in any case, associate in one genus the two forms that have been described as varieties, viz., _palmeri_*, Potts from Texas and Mexico, and _brouini_*, Kirkpatrick from the White Nile. By the kindness of the authorities of the Smithsonian Institution and the British Museum I have been able to examine specimens of all three forms, in each case identified by the author of the name, and I am inclined to regard them as three very closely allied but distinct species. Species with free microscleres similar to those of these three forms but with heterogeneous or tubelliform gemmule-spicules will probably need the creation of a new genus or new genera for their reception. GEOGRAPHICAL DISTRIBUTION.--The typical species occurs in Bombay and Madras; _D. palmeri_ has probably an extensive range in the drier parts of Mexico and the neighbouring States, while _D. brouini_ has only been found on the banks of the White Nile above Khartoum, in Tropical Africa. 17. Dosilia plumosa* (_Carter_). _Spongilla plumosa_, Carter, J. Bomb. Asiat. Soc. iii, p. 34, pl. i, fig. 2, & Ann. Nat. Hist. (2) iv, p. 85, pl. iii, fig. 2 (1849). _Spongilla plumosa_, Bowerbank, P. Zool. Soc. London, 1863, p. 449, pl. xxxviii, fig. 5. _Dosilia plumosa_, J. E. Gray, _ibid._ 1867, p. 551. _Meyenia plumosa_, Carter, Ann. Nat. Hist. (5) vii, p. 94, pl. v, fig. 6 (1881). _Meyenia plumosa_, Potts, P. Ac. Philad. 1887, p. 233. _Ephydatia plumosa_, Weltner, Arch. Naturg. lxi (i), p. 126 (1895).