138 Mr. H. J. Carter on Specimens 



which may be seen the heads of the zone-spicules supporting 

 the dermal sarcode charged with its stellates. Pores in the 

 dermal layer. Vents not seen, probably owing to contraction 

 and dryness. Internal structure very compact on account of all 

 the spicules lying close and nearly parallel to each other as they 

 uninterruptedly converge from the circumference to a point in 

 the centre, where there is no nucleus (fig. 39). Spicules of 

 five forms, viz. : — 1, the zone-spicule, consisting of an ex- 

 tremely long, smooth, slightly curved shaft and trifid head 

 trifurcated, of which the three arms advance obliquely for- 

 wards at an angle of 45° with the shaft, and the rest turn off 

 at right angles to it, shaft 625 by 5-1800ths, head about 30- 

 lSOOths in diameter (fig. 40, a a) ; 2, body-spicule, also ex- 

 tremely long, acerate, smooth, slightly curved fusiform, 625 

 by 4-1800ths (fig. 40, lb) ; 3, forks and anchors largely deve- 

 loped, of which the arms respectively are about 10-1800ths 

 long (fig. 40, c) ; 4 and 5, external and internal stellates, 

 the former about 1- and the latter 4-6000ths in diameter 

 (fig. 40, e,f), both multiradiate and without central nucleus 

 or body — that is, their rays radiate from a central point which 

 is not differentiated, — the internal stellate, as is usual in 

 Stelletta, very faintly developed, and the rays fewer and longer 

 than those of the external one. Largest specimen sessile, 

 about two inches in horizontal diameter at the base and f inch 

 high, somewhat umbonate; but a considerable portion appears 

 to have been left on the rock where it grew. 



Hab. Marine. Free or fixed. 



Loc. Gulf of Manaar. 



Obs. This is a very beautiful species, from the compactness 

 and regularity of its structure internally, which also causes it 

 to closely resemble Tethya cranium (the type of my Tethyina) , 

 hence its designation • but its spiculation is that of a Stelletta. 

 The head of the zone-spicule is subject to great variety in 

 form, sometimes assuming that of the " fork " greatly en- 

 larged (fig. 40, d). It is stated above that a considerable 

 part of the base was probably left on the rock where it grew, 

 since I know by experience, on the S.E. coast of Arabia, that 

 a sponge possessing this kind of structure contracts so forci- 

 bly when alive and fixed on the rock where it may be growing, 

 that it can only be got off in portions with hammer and 

 chisel ! 



Tisiphonia nana, n. sp. (PI. VII. fig. 43, a-e.) 



Laminiform, thin, or filling up the depression in the Melo- 

 besian nodule where it may be growing. Colour white. 

 Surface even. Spicules of four forms, viz. : — 1, large trifur- 



