108 
THE VOYAGE OF H.M.S. CHALLENGEE. 
as 0‘2 mm. Beneath the outer epithelium is a layer of spherasters, chiefly of the smaller 
size already described, though the larger forms are freely mingled with them. 
The choanosomal mesoderm is a darkly staining sarcenchyma ; numerous granule- 
cells are scattered through it. 
The canals are traversed by numerous velar diaphragms, the central aperture of which 
is surrounded by concentrically arranged myocytes ; while fusiform collencytes radiate 
inwards from the margin. The flagellated chambers measure about 0 02 mm. in breadth 
and 0'016 mm. in length. The apopyle is usually wide, O'OllS mm. in diameter. 
The sponge is very nearly related to Calthropella (Pachastrella) geodiides, Carter, 
which differs from it in the character of the calthrops ; in the latter species these 
are provided with dichocladose actines. 
Supplemental Account of all other known Species of Pachasteellida: 
NOT IN THE Challenger Collection. 
Genus Dercitus, Gray. 
Dercitus, Gray, Proc. Zool. Soc. Lond., p. 542, 1867. 
Pachastrella, 0. Schmidt, Spong. Atlant. Gebiet., p. 76, 1870. 
Battersbyia, Bowerbank, Mon. Brit. Spong., vol. iii. p. 347, 1874. 
Pachastrellidse in which the microscleres are spinad microrabds and toxas. 
Dercitus hucMandi (Bowerbank). 
Halina bucMandi, Bowerbank, List Brit. Marine Invert. (Brit. Assoc.), p. 70, 1861. 
Hymeniacidon bucldandi, Bowerbank, Mon. Brit. Spong., vol. ii. p. 226, 1866; voL iii., pi. 
xxxviii. figs. 9-12, 1874. 
Dercitus bucldandi, Gray, Proc. Zool. Soc. Lond., p. 542, 1867. 
Pachastrella bucldandi, 0. Schmidt, Spong. Atlant. Gebiet., p. 76, 1870. 
Dercitus niger. Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. vii. p. 13, pi. iv. figs. 1-6, 1871. 
Battersbyia bucldandi, Bowerbank, Mon. Brit. Spong., vol. iii. p. 346, pi. xcii. fig. 8, 1874. 
Dercitus bucldandi, Norman, Mon. Brit. Spong., vol. iv. p. 93, 1882. 
Sponge. — Massive, sessile. Surface minutely hispid, even. Oscules simple, dispersed. 
Pores inconspicuous. 
Spicules. — I. Megasclere. 1. Calthrops, actines simple, conical, smooth, oxeate, 
0'32 by 0’045 mm. 
II. Microscleres. 2. Toxa, 0’09 by 0‘003 mm. 3. Spinose microrahd, 0'0276 by 
O'OOS mm., including the spines. 
Colour. — When alive dark purple externally, light brown within. Size various, up 
to 50 mm. long by 25 mm. broad, and 25 mm. thick. 
