138 THE VOYAGE OF H.M.S. CHALLENGER. 



Skeleton. — (a) Dermal ; consisting of a layer of irregularly but very thickly scattered 

 tylota ; these spicules may also be found in irregular, short, thick fibres or brushes, 

 disposed at right angles to the surface immediately beneath the dermal membrane, (b) 

 Main; an abundant but very irregular and ill-defined reticulation of spined styli, 

 sparsely echiuated by smaller spined styli. No very distinct fibres are found, although 

 traces of such occur running vertically towards the surface of the sponge. 



Spicules. — [a) Megasdera; of three kinds, (l) Entirely spined styli (PI. XXVII. 

 fig. 12), usually slightly curved and tapering gradually to a very sharp point at the apex ; 

 with the spination distinct but not very strongly pronounced and most developed about 

 the base; size about 0"42 by 0"016 mm.; making up the main skeleton. (2) A few, much 

 smaller, entirely spined styli or subtylostyli (PL XXVII. fig. 12a), usually straight and 

 tapering gradually from the base to a sharp point at the apex, size about 0'16 by '0125 

 mm.; echinating the main skeleton. (3) Tylota (PI. XXVII. figs. 126, 12c), entirely smooth, 

 with straight shaft and not very strongly marked oval heads narrowing towards the end ; 

 size about 0-3 by 0-0094 mm.; the heads of these spicules are often more strongly 

 developed at one end of the shaft than at the other, a character, however, which is by no 

 means peculiar to the species in question. (6) Microsdera ; (1) tridentate isochelse,^ 

 (PI. XXVII. fig. I2d), with only slightly curved shaft; length very variable, up to 

 about 0-04 mm. (2) Slender, usually much contort sigmata, length up to about 

 0'057 mm. 



This sponge comes near to Alyxilla fusca, nobis, but is doubtless distinct, as 

 indicated by the great difference in size of the larger spined styli and perhaps by the 

 absence of echinating spicules in that species ; a very important distinction also lies in 

 the forms of the chelas of the two species {cf. figs. 116 and 12d, PI. XXVIL). 



Locality. — Ofi' Marion Island ; depth, 50 to 75 fathoms. A few fragments. 



Myxilla mariana, var. massa, Ridley and Dendy (PI. XXVIL figs. 6, 6a, 66, 6c, Qd, 



6e, 6/). 



1886. Myxilla mariana, var. massa, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, 



vol. xviii. p. 473. 



Sponge massive, amorphous. The type specimen is irregularly globular in shape 

 and about 37 mm. in diameter. Colour in spirit yellow. Texture soft and spongy. 

 Surface very uneven, but not hispid. Dermal membrane very well developed, thin and 

 transparent. Pores large and exceedingly numerous, plainly visible to the naked eye, 

 collected in large, irregular groups over the subdermal cavities, reducing the dermal 

 membrane in these places to a mere network. Oscula small, scattered, with their 

 margins flush with the surface of the sponge. 



Skeleton. — (a) Dermal; scattered through the dermal membrane are a great number 



1 Occasionally a four-toothed isocliela is found. 



