186 
THE VOYAGE OE H.M.S. CHALLENGES. 
Thus the oxea in these measures 1‘6 by 0‘0237 mm., the rhabdome of the orthotrisene 
1'12 by 0'0355 mm., the cladi are 0’127 mm. in length. No doubt there is considerable 
variation both in the form and size of the spicules of specimens from different localities. 
Bowerbank rests the distinction of the two species, which we have here united under 
one name, on the presence of an ectosomal oxea in the one, and a corresponding tylostyle 
in the other. These different spicules are undoubtedly present, and would, if proper to 
the sponge, more than suffice for specific distinction ; but, as might almost have been 
expected, they form no part of the Stelletta, occurring solely in an incrusting Monaxonid, 
which Bowerbank mistook for a part of the Stellettid cortex. 
The asters are very variable, presenting a vast number of different forms, which pass 
into each other. The chiasters are precisely similar to those of Myriastra from the 
Australian seas. 
Stelletta gruhii, 0. Schmidt. 
Stelletta gruhii, Oscar Scliinidt, Spong. Adriat. Meeres, p. 46, pi. iv. fig. 2, 1862. 
Sponge. — Subglobose, surface hispid; cortex from 178 to 2 '25 mm. in thickness; 
outer layer of the cortex 0‘8 mm. thick, inner layer 1‘6 mm. thick. 
Spicules. — I. Megascleres. 1. Oxea; one variety long and slender, 4‘46 by 
0’015 mm.; the other shorter and thicker, 2'32 by 0’045 mm. 
2. Orthotrisene; rhabdome 2‘856 by 0‘0516 mm., cladi 0*16 mm. long, chord of 
the cladome 0’232 to 0'286 mm. long. 
II. Microscleres. 3. Ectosomal chiaster, with rod-like terminally tylote actines, 
each actine 0‘008 mm. long. 
4. Oxyaster ; no differentiated centrum, actines few, long, conical, sometimes reduced 
to two, when a centrotylote microxea results ; actines of a microtriod or microxea, 
0‘032 mm. ; of varieties in which the actines are very numerous and short,, 0:008 mm. 
in length. 
Colour. — White or grey. 
Habitat. — Quarnero and Zlarin in the Adriatic (0. S.) ; Budleigh Salterton, Devon- 
shire (Carter) ; and Holyhead (Carter). 
Remarks. — In my notes of specimens examined at the British Museum I find the 
dimensions of the rhabdome of the orthotriaene given as 2 ‘06 by 0'039 mm., and of the 
oxea as 2 '3 8 by 0'032 mm. I think these must have been obtained from prepara- 
tions kindly lent me by Dr. E. von Lendenfeld, as I also find a note to the effect that 
the flagellated chambers measure 0‘0237 by 0‘0I58 mm. ; an observation which can only 
have been made from thin slices. These the British Museum does not' possess. 
Mr. Carter, amongst other specimens of Stellettids, seilt me one which' he considered 
