REPORT ON THE MONAXONIDA. 125 



another {e.g., Clathria lohata, Vosmaer, Suherites arciger, Sclimidt, Artemisina suheri- 

 toides, Vosmaer, Amphilectus cqwlliiiis, nobis). 



Locality. — Royal Sound, Kerguelen; depth, 20 to 60 fathoms. Two specimens. 



Amphilectus ceratosus, Ridley and Dendy (PI. XIX. figs. 10, 10a ; PI. XXV. fig. 2 ; 

 PI. XLVII. fig. 2). 



1886. Amphilectus ceratosus, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol xviii. 



p. 350. 



Sponge (PI. XXV. fig. 2) massive, lobate, sessile, of very irregular shape. The 

 largest specimen is 44 mm. long and varies much in diameter. Colour in spirit dark 

 reddish-brown. Texture spongy, elastic, but fairly compact. Surface uneven, with 

 small, angular conuli, but glabrous. Dermal membrane rather thick, granular and of a 

 brown colour, peeling off fairly easily. Oscula small and scattered, not noticeably 

 elevated above the general surface of the sponge. 



Skeleton (PI. XLVII. fig. 2). — (1) Horny, consisting of a well-developed reticulation 

 of ramifying and anastomosing horny fibre, without any spicular core. This horny fibre 

 is doubtless the most important part of the skeleton functionally; it averages about 0*07 

 mm. in thickness. (2) Spicular — {a) Dermal; consisting of numerous, irregularly 

 scattered tylote spicules, {h) Main; consisting of similar, irregularly scattered tylote 

 spicules ; there is no spiculo-fibre in the deeper parts of the sponge though the scattered 

 spicules are everywhere abundant, but towards the surface the spicules are often collected 

 into loose wisps. 



Sjncules. — (a) Megasclera; of one kind only; viz., straight, entirely smooth tylota 

 (PL XIX. fig. 10), with a distinct oval head at each end of the slender shaft; size about 

 0"24 by 0"003 mm. (6) Microsclera; of one kind only ; viz., isochelse (PI. XIX. fig. 10a), 

 profusely scattered both in the dermal membrane and in the deeper parts of the sponge ; 

 length about 0'025 mm. 



This sponge is extremely interesting on account of the existence in it of a well- 

 developed horny skeleton. We at first thought that this might be due to the joresence of 

 a Euspongia over which the Amphilectus had grown, but there are in the collection three 

 specimens, and there is not the slightest reason to suppose that the horny fibre is not 

 proper to the species. The absence of a spicular core to the fibre must be especially 

 noticed. Coincidently with the development of a horny skeleton we have great reduction 

 in the spicular skeleton, and it is possible that we have in this species an actual transi- 

 tional form between the Siliceous and Keratose sponges. The isochelate spicules, however, 

 are very abundant throughout the sponge, and appear to have suffered no diminution in 

 numbers. It is provisionally only that we include this sponge in the genus Amphilectus, 



