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



Myxilla paucispinata, Eidley and Dendy (PL XXVII. figs. 2, 2a, 2b, 2c ; PI. XXX. 

 fig. 3). 



1886. Mijxilla paucispinata, Eidley and Dendy, Anii. and Mag. Nat. Hist., ser. 5, 



vol. xviii. p. 471. 



Sponge (PI. XXX. fig. 3) massive, amorphous, cavernous.' Colour m spirit pale yellow. 



Texture rather soft, very In-ittle and fragile. Surface very uneven and roughly hispid 



from the presence of numerous large foreign (Hexactinellid) spicules ; with numerous 



apertures leading into canals ; some of these apertures are undoubtedly oscula, each being 



surrounded by a fringe of spicules. The surface also presents circular areas, in each of 



which the parchment-like dermal membrane covers over an underlying cavity ; these 



are possibly in part pore-areas, but we have not succeeded in demonstrating the fact, 



and have offered below what seems to be a more likely explanation of their presence. 



The Oscula are in the centres of similar looking areas and are thickly fringed by radiating 



brushes of tylote spicules, which occur chiefly in this position and also, in fewer 



numbers, in the circular areas above mentioned. Pores (?). 



Skeleton. — (a) Dermal ; a close, irregular reticulation of large stylote spicules similar 



to those of the main skeleton, with a small admixture of tylota.^ Within a certain radius 



of the oscula the stylote spicules abruptly and entirely disappear and give place to 



thick brushes of the tylota ; these converge towards the osculum, the margin of which is 



fringed by the free ends of the terminal spicules of the brushes. The stylote spicules 



are also absent from the circular areas above described, their place being taken by a few 



tylota which sometimes show an incipient radiate arrangement ; from these considerations 



it seems not improbable that some, at any rate, of the spaces mentioned mark the 



positions of future oscula. {b) Main ; this consists of an irregular but close reticulation 



of stylote spicules in which no fibre is developed. 



Spicules.— {a) Megasclera; of two kinds, (l) Large, stout styli (PI. XXVII. fig. 2) 



usually curved, with rather blunt apex and not infrequently slightly spined ; size about 



07 by 0-031 mm. (2) Tylota (PI. XXVII. fig. 2a) each with a fairly straight shaft bearing 



a distinct, though only slightly developed, oval head at each end ; entirely smooth ; size 



about 0-4 by 0-008 mm. [b) Microsclera; of two kinds, (l) Tridentate isochete 



(PI. XXVII. figs. 2b, 2c), with stout, strongly curved shaft ; length about 0-05 mm. 



(2) Slender sigmata, simple and contort, varying a good deal in size, up to about 



0-056 mm. long. 



Unfortunately there is only a single piece of this sponge in the collection, and 



that in very poor condition. It is encrusted in places by a thin, black, coating sponge 



1 ^\'■ith embedded Polychjete wormi;, to which the exceedingly cavernous nature may be in part due. One large 

 tunnel penetrates right through the sponge, which is perhaps only a fragment. 



2 It is possible that the tylota alone form the true dermal skeleton and that the styli are merely an upper layer 

 of the main skeleton ; this would explain the absence of styli immediately around the oscula. Compare with this 

 the dermal skeleton in Myxilla cribrigcra, nobis. 



