438 
THE VOYAGE OF H.M.S. CHALLENGEE. 
species, Tethya morum and Tethya lyncurium ; the latter with two varieties, besides 
the type, occurring in the Adriatic. Subsequently (1868) he suppressed Tethya 
morum, regarding^ it as identical with Tethya lyncurium. In this I have no doubt he 
was right, and the varieties may d fortiori be suppressed too. 
The northern form, Tethya norvagica, Bowerbank {Tethya lyncurium, var. ohtusum, 
Vosmaer ?), is distinguished from the Mediterranean by its smaller size. Bowerbank exam- 
ined a considerable number of specimens, and states that they vary from 4 to 15 mm. in 
diameter ; and Dr, Norman’s specimens, which I have examined, seldom exceed 5 or 6 mm. 
The cortex is comparatively thin, less than 1 mm, in thickness ; and in a fragment of 
one of Bowerbank’s types the spicules measured as follows ; — Strongyloxea 1 “6 by 
0'0193 mm.; cortical spheraster 0'04 mm. in diameter; somal aster 0’012 mm. in 
diameter. The last named spicule exhibits a curious tendency to pass into a globule, 
with a somewhat nodose surface ; this results from the reduction of the actines, rather 
than the overgrowth of the centrum, though both are concerned. In Dr. Norman’s 
specimens the cortical spheraster is larger, 0'058 mm. in diameter, and is distinguished 
by the tendency of the actines to dichotomise. The examples from the British seas, 
though frequently larger than those from Norway, do not seem to be characterised by 
larger spicules. Thus a specimen I obtained from Koscoff measured about 25 mm. in 
diameter, and its cortex 4 mm. in thickness, but the spicules are scarcely larger than 
those in Dr. Norman’s Norwegian specimens. Thus the strongyloxea measures 1’7 by 
0‘026 mm., and the cortical spheraster 0'058 mm. in diameter. 
Bowerbank does not give measurements of the spicules in the British specimens he 
examined, but measurements taken from his drawings almost exactly correspond with 
those of my Eoscoff specimen. He gives the thickness of the cortex as varying from 
2 to 6 mm. 
The Mediterranean examples are characterised by much larger spicules than the 
Norwegian and British. From a portion of one of 0. Schmidt’s types I obtained the 
following measurements : — Strongyloxea 2 '54 by 0'0387 mm.; cortical spheraster 
0‘097 mm. in diameter; somal aster 0 ‘02 mm., in diameter. It would appear possible, 
therefore, that three varieties may eventually be distinguished, — the type-species, 
characterising the Mediterranean, a South British variety and a North British and 
Norwegian variety. 
Tethya histellata, 0, Schmidt. 
Tethya histellata, O. Scliinidt, Spong. Adriat. Meeres, p. 45, pi. vii. fig. 1, 1862. 
Sponge. — As in Tethya lyncurium. 
Spicules . — I, Megasclere. 1. Tylotoxea. 
II. Microsclere. 2. Spheraster, partly of the usual form, partly with the actines 
