90 
THE VOYAGE OF H.M.S. CHALLENGER. 
from SpJiinctrella cnhrifera. A thin membrane forms the distal part of the cloacal tube, 
and through this in a layer but one spicule thick the fringing oxeas (chiefly form No, 2) 
proceed to the exterior. The membrane is further supported by a thin felt of the annulated 
microxeas, which are more abundant here than elsewhere. In the choanosome the smooth 
microxeas chiefly contribute to the felt, though the annulated forms are far from 
infrequent. 
Sphinctrella ornatus, n. sp. (PI. XLII. figs. 3, 4). 
Sponge, incrusting, oscules large, circular, surrounded with a fringe of long oxeas, 
which lie prostrate over the oscule, completely concealing it ; pores (?) ; surface covered 
with long prostrate oxeas. 
Spicules. — I. Megascleres. 1, Oxea, stout, fusiform, usually curved, not sharply 
pointed, 3 ‘2 by 0‘08 mm. 
2. Oxea, long, slender, cylindrical, sharply pointed; 4‘3 mm. by O'OIS mm. This 
spicule is that which fringes the oscular margin. 
3. Calihrops (?), It is doubtful whether this spicule is present ; out of seven or eight 
preparations only one or two instances were met with, and these may have been accident- 
ally introduced from specimens of SpJiinctrella gracilis, which are preserved in the same 
bottle. 
II. Microscleres. 4. Microtriod (PI. XLII. fig. 3), the three actines usually make 
an angle of 120° with each other, but occasionally two of them are paired, as in the 
sagittal triradiate of the Calcispongise. Sometimes an additional actine is present, and 
the spicule becomes a microcalthrops ; more rarely an actine is suppressed and a diactinate 
form results, which may be a microxea or not. The most remarkable feature of this 
spicule is the presence of a ridge-like thickening of the actines, giving to their marginal 
outline a spined appearance. The ridge winds round the actine spirally or forms a series 
of transverse rings. It is minutely spined on the summit. In an average example the 
spire made one complete revolution in a distance of O’Ol mm. measured along the length 
of the actine, the diameter of the actine being 0‘014 mm., and its total length 0T6 mm. 
In the smallest annulated triod the actines measured 0’06 mm., in the largest 0'2 mm. 
in length. 
5. Microcalthrops, the actines are slender, roughened by minute granules and sharply 
pointed; occasionally a fifth actine is present; the actines measure 0’06 mm. in length. 
6. Spiraster (PI. XLII. fig. 4), the spire is concealed by the spines, which are 
long and numerous, total length 0’0276 mm., of a single spine O’OllS mm. 
7. Metaster ; this is a very variable spicule, usually of comparatively large size ; an 
amphiastral variety with only four spines at each end measured altogether 0'035 mm. 
in length ; the spines 0'016 mm.; in a genuine metastral form with long slender spines. 
