REPORT ON THE MONAXONIDA. 137 



membrane to a network, but we have found no perfect examples of this arrangement. 

 Oscula small and scattered, having their margins usually sunk a little below the general 

 surface of the sponge. 



Skeleton. — (a) Dermal; consisting of a very irregular layer of tylote spicules, 

 scattered, or in loose bundles and brushes which may commence beneath the surface 

 and project outwards, (b) Main ; a very irregular reticulation of entirely spined styli. 

 No very distinct fibres are present, although primary lines of spicules may be recognised, 

 with little difficulty, running vertically towards the surface. 



Spicules. — («) Megasclera; (1) entirely spined styli (PI, XXVIl. fig. 11), with the 

 spination well marked, usually slightly curved and sharply pointed at the apex, size 

 about 0-52 by 0-034 mm. (2) Tylota (PI. XXVIL fig. 11a), with heads only faintly 

 developed, entirely smooth, with straight shaft and weU-rounded ends, size about 0'42 by 

 O'Ol mm. We have not found any distinct echinating spicules, although sometimes 

 entirely spined styli, much smaller than those described, occur, which may perhaps 

 represent them, {h) Microsclera ; (1) tridentate isochelae (PI. XXVIL fig. 116), with 

 strongly curved shaft and of rather peculiar shape, length about 0'047 mm. (2) Very 

 slender sigmata, usually much contort, length about 0'05 mm. Neither kind of microsclera 

 occurs very abundantly. 



This sponge, represented in the collection only by two small pieces, closely resembles in 

 external appearance an lophon, and may readily be distinguished from other Myxillse by 

 its dark colour (should this prove to be a constant feature of the species). It is 

 distinguished from Myxilla paupertas, Bk., and Myxilla nobilis, nobis, by the presence 

 of the sigmata, the entire spination of the large stylus, and the absence of the 

 echinating stylus ; and from the latter also by the fact that the tylota are smoothly 

 rounded ofi" at the ends. The sponge contains a considerable amount of foreign matter, 

 chiefly Foraminifera. 



Xoca%.— Station 150, February 2, 1874; lat. 52° 4' S., long. 71° 22' E.; west of 

 Heard Island, Southern Ocean; depth, 150 fathoms; bottom, coarse gravel; bottom 

 temperature, 35° "2. Two specimens. 



Myxilla mariana, Ridley and Dendy (PI. XXVIL figs. 12, 12a, 12&, 12c, I2d). 



1886. JfyxiWa manana, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 472. 



Sponge massive ; represented in the collection only by a few fragments, the largest of 

 which is about 25 mm. long by 12 mm. broad. Colour in spirit very pale, yellowish- 

 grey. Texture fairly compact, but soft and rather crumbling. Surface smooth, more or 

 less glabrous, but very uneven and deeply furrowed by wide meandering grooves, so as to 

 give rise to a number of irregular, stumpy lobes. Dermal membrane thin, transparent, 

 adhering rather firmly to the underlying tissues. Pores; these appear to be rather 

 scarce, and we have observed no definite pore-areas. Oscula small and scattered. 



(ZOOL. CHALL. EXP. PAET LIX. — 1887.) Nmi 18 



