248 
THE VOYAGE OF H.M.S. CHALLENGEE. 
Geodia megastrella, Carter. 
Geodia megastrella, Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xviii. p. 400, pi. xvi. fig. 46, 
1876. 
Sponge. — Hemispherical, elongate, flattened at the base, attached. Oscule on the 
summit. Cortex, 0’876 mm. thick, ectochrote very thin, cortical oxeas rare. 
Spicules. — I. Megascleres. 1. Somal oxea, 2'95 by 0‘042 mm. 2. Cortical oxea, 
0’191 and over by 0 007 mm. 3. Orthotrisene, occasionally replaced by a dichotrisene, 
rhabdome 2'8 by 0‘07 mm., cladi 0‘67 by 0‘07 mm. 4. Ana- and 5. Pro-trisene, similar 
to those of Geodia harrettii, var. nodastrella, Carter. 
II. Microscleres. 6. Sterraster, ellipsoidal, 0183 mm. in diameter. 7. Somal 
chiaster, very variable, actines short, cylindrical, strongylate, or tylote ; sometimes a 
small centrum is present, O'OOS mm. in diameter. 8. Choanosomal oxy aster, with from 
three to eight long, conical actines, minutely spined, a single actine 0'063 by 0’004 mm. 
Colour. — Grey in the dried state. 
Habitat. — Station 25, “Porcupine” expedition, 1870, near Cape St. Vincent; depth, 
374 fathoms. 
Remarhs. — The size of the sterraster and the characters of the somal chiaster distin- 
guish this from Geodia harrettii, var. nodastrella. Carter. In my sections the cortex also 
has a very difierent appearance to that in the last-named species, owing to the thinness 
of the ectochrote and the absence of brushes of cortical oxeas, which only occur singly. 
Geodia (f) megastrella, var. levispina, Carter. 
Geodia megastrella, var. levispina. Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xviii. p. 401, 
pi. xvi. fig. 47, 1876. 
This variety is founded on a fragment of the cortex, about 25 mm. square, with a little 
of the choanosomal tissue adherent. The sterraster is intermediate in size between 
that of Geodia nodastrella and Geodia megastrella, viz., 0154 mm. in diameter, 
and the actines of the oxyaster are smooth, not spined. The orthotrisene is said to be 
smaller than that of the last-named species, but it is obviously impossible to obtain 
reliable measurements from such a small fragment as that which Carter had under 
examination. 
Geodia plaeenta, 0. Schmidt. 
Geodia placenta, 0. Sclimidt, Spong. Adriat. Meeres, p. 49, pi. iv. fig. 7, 1862. 
Sponge. — Tuberose, depressed, or forming thick, incrusting, cake-hke masses ; surface 
flnely or densely hispid ; cortex from 1 to 3 mm. in thickness, consisting of an ecto- 
