REPOET ON THE TETRACTINELLIDA. 
267 
Remarks. — This is a very distinct species of Synops, characterised by more than 
usually large megascleres. As in all other species of the genus anatrisenes are absent, 
or if present so remarkably rare that they may be disregarded. I saw one or two 
cladal ends of these spicules in the choanosome, they were evidently foreign to the 
sponge and had been incorporated ; possibly the presence of those mentioned by Vosmaer 
is to be similarly explained. The chamber system, of which Vosmaer professed to be 
unable to make out all the details, is precisely similar in all respects to that of other 
members of the genus ; this and the dimensions of the spicules I was able to ascertain by 
examination of a fine specimen which I owe to the kindness of its describer. 
Genus Isops, Sollas. 
Section Ditrisena. 
Isops pklegrsei, Sollas. 
Isops phlegree.i, Sollas, Ann. and Mag. Nat. Hist., ser. 5, vol. v. p. 396, pi. xvii. 
Sponge. — More or less spherical ; surface hispidated by projecting megascleres. 
Cortex about 0’64 mm. in thickness, consisting chiefly of the sterrastral layer, both the 
inner fibrous layer and the ectochrote being very thin, the latter containing a layer of 
somal spherasters. Oscules and pores similar, small. 
Spicules. — I. Megascleres. 1. Oxea, 6 by 0'063 mm. 2. Plagiotrisene, rhabdome 
4 by 0'425 mm., cladi 0’6 mm. in length ; sometimes becoming dichocladose. 3. Pro- 
trisene, rhabdome long, 0'02 mm. in diameter. 4. Anatrisene, rhabdome similar. 
II. Microscleres. 5. Sterraster, ellipsoidal, 0’09 mm. in diameter. 6. Somal spher- 
aster, centrum comparatively small, actines conical, oxeate numerous, diameter 0'012 mm. 
7. Choanosomal spheraster, centrum comparatively small, actines long, conical, oxeate, 
somewhat numerous, from 0'02 to 0‘07 mm. in diameter. 
Colour. — Faint grey. Size, 25 mm. 
Habitat. — Kors Fjord, Norway (Norman) ; depth, 180 fathoms. 
Isops phlegrsei, Sollas (?). 
Isops pallida, Vosmaer, tom. cit., p. 16, pi. i. figs. 9, 15; pi. ii. figs. 22-26, 29-38 ; pi. iv. 
fig. 117, 1882. 
Sponge. — Ellipsoidal or pyriform, the basal part bears small papillary processes (traces 
of roots, Vosmaer). 
Spicules. — I. Megascleres. 1. Oxea. 2. Tylotoxea. 3. Orthotrisene. 4. Dicho- 
trisene. 5. Anatrisene. 
