308 
THE VOYAGE OF H.M.S. CHALLENGER. 
about 0‘16 to O' 24 mm. in diameter, situated at the summit of conical monticules, about 
I'O mm. wide at the base. The ectosomal dichotrisenes extend over the sides of the 
monticules, but stop short at the summit ; the interior of the crater is lined by the 
strongylospires and associated spirasters, which lie beneath a thin outer skin. This 
spicular layer is continued down the sides of the tube, which descends into the sponge 
from the oscule. 
The poral tubes are each surrounded by a skeletal wall formed of desmas, and end at 
the surface each in a little crateriform depression, lined by a spicular layer like that of 
the oscules. The pore is simply the open end of the poral tube ; it is usually about 
0'032 mm. in diameter, and the depression in which it lies about 0T6 mm. across. 
The dichotrisene recalls to mind that of Corallistes noli-tangere, as figured by 
Schmidt. Zittel’s illustration of this spicule differs from Schmidt’s, and is altogether 
unlike that of Corallistes thomasi. The strongylospire is the homologue of the micro- 
rabd which occurs in other species of Corallistes, it is possibly not truly spiral, but 
merely undulating, and if so, should be termed a sinuous strongyle. 
Corallistes bowerhanJci, Johnson. 
Dactylocalyx bowerhaiM, Johnson, Proc. Zool. Soc. Lond., p. 257, 1862. 
„ ,, Bowerbank, Proc. Zool. Soc. Lond., p. 94, pi. vi. figs. 5-8, 1869. 
„ „ Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xii. pp. 437, 441. 
Corallistes howerhanki, Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xviii. p. 460, 1876. 
Corallistes typns, Zittel, Abhandl. d. k. baier. Akad. d. Wiss., vol. i. pp. 103, 120, 1878. 
The specimen, which I believe I am right in assigning to this species, is but a part of 
the wall of a sponge which in the complete state must have been of very considerable 
size. It had evidently been lying in a dead state on the sea-floor for a long time before 
it was dredged up, consequently microscleres are not present, and the ectosomal trisenes 
have suffered considerably from solution. The fragment is a plate-like slab, bounded by 
broken edges on two sides, and on the third by the natural margin, which is not rounded 
but irregularly ridged. It measures 96 by 112 mm. and is 16 mm. thick. On the poral 
surface exposed superficial canals are seen with a general longitudinal drift towards the 
margin. Both excurrent and incurrent canals, which are about 0'5 mm. wide, wander 
crookedly but transversely through the wall. 
The desmas differ markedly from those of Corallistes masoni, Bowerbank, they are 
usually smooth, tubercles only appearing here and there on the sides of the epirabds 
and cladi, which end by breaking up into numerous twig-like processes with expanded 
ends. The interlocking of the , desmas takes place by means of these processes, and in 
general character much resembles that of the Tetracladidae ; the quadriradiate form of 
some of the desmas is also very striking, but all are founded on a monaxial spicule. 
The ectosomal spicules are dichotrisenes, the conical rhabdome measures 0‘72 by 
