REPORT ON THE MONAXONIDA. 35 



Localltij.—Q.) Station 135, October 15, 1873 ; lat. 37° 1' 50" S., bug. 12° 19' 10" AV. ; 

 Tristan da Cunha ; depth, 360 fathoms ; bottom, volcanic sand. 



Habitat. — Singapore (Carter); Prince of Wales Channel, West and Alert Islands, 

 Torres Strait (Ridley) ; (?) Tristan da Cunha (Challenger). 



RMzochalina pedunculata, Eidley and Dendy (PI. VIII. fig. 1 ; PI. IX. figs. 2, 6). 



1886. RMzochalina pedunculata, Ridley and Dendy, Ann. and Slag. Nat. Hist., ser. 5, vol. xviii. 



p. 332. 



Sponge (PI. VIII. fig. 1) irregularly rounded, slightly elongated, with one end drawn 

 out into a short, stout peduncle, to the extremity of which is firmly attached a quantity 

 of black sand. The sponge has evidently lived in an erect position, attached to the 

 bottom by the peduncle. Height, inclusive of peduncle, 40 mm. ; breadth 25 mm. Un- 

 fortunately, a portion of the peduncle is broken ofi" obliquely, leaving only a fragment of 

 the base. Irregularly scattered over the surface of the sponge occur a number of fistul^e, 

 about 4 mm. in diameter, all broken off (? some naturally terminating) close to the surface 

 of the sponge, so as to present the appearance of so many oscula ; nine such fistulte are 

 present, varying a little in width. Colour of the body a dirty brownish-yellow. The 

 bast-layer and dermal membrane together form a very thin coating to the sponge, no 

 thicker than a sheet of writing paper, which readily peels off from the underlying tissues. 

 Surface slightly rough and wrinkled. Texture firm and compact throughout. Wide 

 canals penetrate right to the centre, converging and opening into the bases of the fistula, 

 which probably act as oscular tubes. 



Skeleton. — Arranged as in Rhizochalina Jistulosa, with (a) a dermal network of chiefly 

 oxeote spicules, lying immediately below the thin, transparent external membrane. The 

 spicules of the dermal network vary very greatly in size and form. We have (l) sausage- 

 shaped (strongylote) spicules (PI. IX. fig. 2) with rounded ends, nearly straight or very 

 slightly curved, measuring 0'106 by O'Ol mm., 0*23 by 0'013 mm., 0'19 by 0'017 mm., 

 &c. It is not uncommon to find smaU strongylote spicules with a central bulbous 

 inflation (PL IX. fig. 2, h, c) ; these are probably young forms. (2) More numerous, 

 oxeote spicules, nearly straight, or slightly curved, sometimes becoming blunted at the 

 end, varying greatly in size, from 0"09 by 0"0047 mm. to 0'25 by 0'009 mm. (There 

 can be little doubt that the smaller spicules are here, as in other cases, simply young 

 forms, which have not yet attained their maximum size.) (6) A bast-like reticulation 

 of spiculo-fibres, which in this species forms only a very thin layer, consisting of a uni- 

 lamellar network of fibres, comj)osed of oxeote (and strongylote ?) spicules similar to those 

 forming the dermal network. The fibres are very compact, averaging about O'l mm. in 

 diameter. (c) A rather scanty reticulation of spiculo-fibres, ramifying through the 

 interior of the sphere and supporting the canal system. Also a great number of loose 



