KEPORT ON THE TETRACTINELLIDA. 
127 
Pilochrota tenuispicula, Sollas (PL XV. figs. 28-32). 
Pilochrota tenuispicula, Sollas, Prelim. Account, Sci. Proc. Roy. Dubl. Soc., vol. v. p. 190, 1886. 
Sponge (PI. XV. fig. 28), small, irregularly spherical, free. A single comparatively 
large oscule on the upper surface, with a membranous margin, leading into a large and 
deep cloaca, on the walls of which numerous excurrent canals open. Surface smooth, 
partly incrusted with foreign bodies raised into a honeycomb-like reticulation of smooth 
ridges ; in the depressions between these, the pore-sieves, overlying the chones, are 
situated. 
Spicules. — I. Megascleres. 1. Oxea (PI. XV. fig. 29), varying from a stout, fusi- 
form, somewhat sharply pointed variety to a slender anisoactinate form, having its 
greatest diameter nearer the distal than the proximal end, from 1‘35 to 2’3 by 0‘16 mm. 
2. Orthotriaene (PI. XV. fig. 30). Ehabdome slender conical, attenuated to very 
sharply pointed proximal extremity ; cladi simple, conical, and extending horizontally 
almost immediately on leaving the rhabdome, frequently crooked, and otherwise crippled. 
Ehabdome 1‘6 by 0'16 mm., cladi 0H2 mm. long. 
II. Microsclere. 3. Chiaster (PI. XV. fig. 31), rare, a small but evident centrum 
and very slender actines, not tylote ; 0‘012 mm. in diameter. 
Colour. — Puce-grey. 
Habitat. — Bermuda . 
Remarhs. — There is a single specimen of this sponge, 14 by 11 mm. in width and 
breadth, and 10 mm. in height. The single oval oscule measures 3 by 1'5 mm. in 
diameter. 
Ectosome. — The cortex (PI. XV. fig. 32), from 0'5 to 072 mm. in thickness, consists 
chiefiy of fusiform fibres distributed as in Pilochrota pachydermata ; beneath the outer 
epithelium is a layer of variable constitution, 0'02 mm. thick; it is not clearly defined from 
the rest of the cortex, but appears as in the other species of this genus to consist of the col- 
lenchymatous matrix which forms the basis of most of the tissues, freer in this case of cellular 
elements than elsewhere ; the gelatinous basis is stained by hsematoxylin, and contains in 
addition to tangentially disposed fusiform cells (though these are sometimes absent), either 
the minute vesicular cells, about 0'009 mm. in diameter, previously described, or minute 
oval protoplasmic bodies, about 0'003 mm. in diameter, which may be the protoplasmic 
parts of the vesicular cells without the enclosing vesicle ; these little bodies are prolonged 
into a slender, darkly stained fibril, which proceeds from their distal end towards th^ 
outer epithelium, 0‘02 mm. distant, against which it terminates. Similar bodies occur 
in many other sponges, and some are figured from the ectosome of Azo?'ica pfevfferse 
(PL XXXVI. fig. 22). Beneath this outermost layer occur the round oval clusters or balls 
of cells, which appear to be constantly present in species of this genus. They may 
