REPORT ON THE MONAXONTDA. 213 



it bears eight or nine fistulse, varpng from minute buds to processes measuring about 

 13 mm. in length and about 2 mm. in diameter. Tlie smaller specimen bears only 

 a single long process. Colour in spirit (where the surface is visible) almost white. 

 Texture of the body, firm, very gritty; of the processes, firm, compact, rather stiff. 

 Surface roughened on the body with the foreign objects ; smooth and glabrous-looking 

 on the fistular processes, Ijut in reality very minutely hispid. Oscula and Pores both 

 doubtfully observed, but we have reason to believe, from the examination of our pre- 

 parations, that numerous small openings in the walls of the fistular processes lead from 

 the outside into the central canal. 



Skeleton. — (a) Of the main Ijody ; as in other species of the genus there are stout 

 columns of spiculo-fibre (PI. XLII. fig. 1, c), running vertically towards the surface, where 

 they expand more or less. The special dermal layer (PI. XLII. fig. 1, a), composed of 

 dense brushes of small stylote spicules, so characteristic of the genus, is almost absent 

 over the body, being replaced functionally by large grains of sand (PI. XLII. fig. \,h), 

 fragments of shell and so forth ; yet it can be found in the crevices between these 

 foreign bodies. The skeleton fibres are composed of large, stout styli or subtylostyli, 

 and in the interspaces between them numerous small tylostyli (PL XLII. fig. 1, d) are 

 scattered, very abundant near the surface, but rare lower down. {Ij) Of the fistular 

 projections ; here the skeleton is very regularly and symmetrically arranged ; beginning 

 at the outside there is a very dense dermal crust (PI. XLII. fig. 3, a) of small tylostylote 

 spicules, arranged vertically to the surface, beyond which their apices project for a very 

 short distance. This crust is not quite continuous all over the surface, but arranged 

 in a reticulate manner, so as to leave interspaces in which probably the pores are 

 situate. Immediately beneath this layer comes a layer (PI. XLII. fig. 3, h) of larger 

 spicules, lying parallel (more or less) to the surface and also arranged in a reticulate 

 manner, so as to leave interspaces corresponding to those in the dermal crust. This 

 layer is not very thick and immediately below it comes a series of stout, longitudinal 

 bands of spiculo-fibre (PI. XLII. fig. 3, c), about ten or twelve in number, and arranged 

 in a circle against its inner surface, like a series of buttresses against the inside of a wall ; 

 then come the soft tissues, almost devoid of spicules excepting immediately around the 

 central canal, where small tylostyli are sometimes abundantly scattered (PI. XLII. fig. 

 3, d). The structure of the stout fibres in the fistular processes appears to be exactly 

 the same as in the body of the sponge. 



Spicules. — Megasclera; (1) large, straight styli or subtylostyli (PI. XLII. fig. 2), 

 very gradually and finely pointed at the apex and narrowing somewhat towards the base ; 

 size up to about 1'2 by 0'0157 mm. (2) Very small, usually slightly curved, slender 

 tylostyli (PI. XLII. figs. 2a, 26), with well-developed heads and fairly sharp apices ; 

 size about 0"175 by 0*004 mm. More or less intermediate forms also occur, e.g., in the 

 layer beneath the dermal crust, but the two chief forms are very distinct from one another, 



