134 
THE VOYAGE OF H.M.S. CHALLENGER. 
diameter, and leads into a tubular cloaca about 3 mm. in depth. Its systematic position is 
a matter of much perplexity. The choanosomal chiaster may be regarded as foreshadowing 
the anthaster of other Stellettids, and it may be preferable to assign the sponge to the 
genus Anthastra. The cortex is thin compared with most species of Pilochrota, from 
0‘32 to 0'48 mm. in thickness, but since the outer layer to the thickness of 0‘24 to 
0'32 mm. consists of fibrous tissue, its place would seem to be with this genus. The 
inner layer of the cortex, from OTO to 0’24 mm. thick, but not always present, consists of 
collenchyma in which, however, fusiform cells are usually present in more or less abund- 
ance. In the outer fibrous layer oval or round balls of granule-cells are present in 
considerable numbers ; they are about OT mm. in diameter. The pores lead either 
immediately or by communicating canals into the chones, which are about 0’08 to 
0T6 mm. in diameter, and usually open by wide unconstricted apertures into large 
incurrent canals, the roots of which frequently extend tangentially beneath the cortex. 
In one of these tangential extensions an Annelid, 0'24 mm. in diameter and over 2‘0 mm. 
in length, was observed ; it was evidently living when the sponge was placed in spirits, 
and from the neatness with which it fills the canals, looks very much like an inhabitant. 
The chones are frequently crossed by velar diaphragms, at the level of the inner surface 
of the fibrous layer and sometimes at other levels. Concentric myocytes surround the 
lumen of the diaphragm, and small fusiform cells, about 0’04 mm. in length, may some- 
times be seen radiating from it ; similar cells extend inwards from the sides of the 
chones ; in both cases the outwardly directed end of the cell stands in contact with the 
free epithelial surface. In one case a conical cell, with a base about 0'004 mm. wide 
applied against the epithelium, was observed ; the conical body of this cell measures 
0'008 mm. in length, is produced inwards into a delicate fibril 0*012 mm. long, and 
presents at the middle a well-marked oval nucleus, 0*004 mm. in length, containing a 
small spherical nucleolus. 
The fiagellated chambers measure 0*024 by 0*02 mm. in breadth and length. The 
canals, both excurrent and incurrent, contain large quantities of finely granular material, 
pointing to the fact that the animal was actively feeding at the time it was captured. 
The choanocytes, 0*004 mm. in diameter at the base, are deeply stained, and the proto- 
plasm of the base appears more than usually granular. 
Pilochrota lendenfeldi, n. sp. (PI. VII. fig. 5). 
Sponge (PI. VII. fig. 5) more or less spherical, supported on a short stalk ; no visible 
oscules ; pores in sieves generally distributed. Cortex comparatively thin. 
Spicules. — I. Megascleres. 1. Oicea, stout, fusiform, usually curved, sharply pointed, 
2*5 by 0*0434 mm. 
