REPORT ON THE TETRACTINELLIDA. 
93 
The ectosome is only distinguished from the choanosome by the absence of flagellated 
chambers. 
The mesoderm is a finely granular collenchyme, which in the immediate neighbour- 
hood of some of the larger canals becomes clear of granules, cavernous, and traversed 
by a few fusiform cells. The flagellated chambers are eurypylous, from 0'0276 to 
0‘031 by 0‘039 mm, in diameter. The choanocytes are about 0’004 mm. broad at the 
base, and 0'006 mm. high, the fenestrated membrane in which their distal ends terminate 
is more clearly marked than the outer wall of the chamber. 
The pores vary from about 0'06 to 0T6 mm. in diameter ; the oscules are about 2 to 
3 mm. in diameter. 
The chief interest in this sponge lies in the rarity of its tetractinellid or trisene 
spicules, the trisenes of the surface are few and easily overlooked ; so difficult, indeed, are 
they to find that at first I was in some doubt as to whether the sponge really possessed 
them, or belonged to the Tetractinellida at all ; some fragments 8 mm. square and 4 mm. 
thick yielded no trisenes when boiled with nitric acid ; and it was only by finding them 
in position in the sponge that I arrived at certain conclusions. They are best found 
by examining the hispid surface with a powerful simple lens, or by slicing off a part 
of the superficial lajmr of the sponge with a razor and examining it en face. 
The sponge is evidently very nearly allied to Pcecillastra; indeed, I feel by no means 
sure that it differs sufficiently for generic distinction ; further discoveries will determine 
this. By the disappearance of trisenes or calthrops from the interior, a certain resemblance 
to Stryphnus is produced, which differs, however, by the presence of true asters, in 
possessing a cortex, and in the substitution of a sarcenchymatous for a collenchymatous 
mesoderm. 
Genus 5. Triptolemus,'^ n. gen. 
Theneidse in which the characteristic megasclere is a mesotrisene. The microscleres 
are similar to those of Normania, but the microxeas are of hair-like thinness and entirely 
spined. 
Triptolemus cladosus, n. sp. (PI. XXXV. fig. 23). 
Samus quadripartita, MS., Carter. 
Sponge . — Small, incrusting. 
Spicules . — I. Megascleres. 1. Oxealf). 
2. Mesotrisene (PL XXXV. fig. 23) tetracacladose. Ehabdome with conical similar 
actines, not sharply pointed ; the length of .the actines could not be exactly ascertained, 
^ By a singular omission, which I hasten to supply, no one so far as I can ascertain has yet honoured Triptolemus 
with a genus. 
