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



themselves, are visible to the naked eye. Diameter of pore-areas about 1 mm.; of the 

 pores themselves very variable, averaging about 0"1 mm., but may be much greater. 



Skeleton. — (a) Dermal ; when pieces of the dermal membrane are peeled off from the 

 surface of the sponge, as is easily done, and examined separately, the only true skeleton 

 they possess is seen to consist of rather sparsely scattered tylote spicules ; some- 

 times, however, the styli belonging to the underlying main skeleton project beyond 

 the surface of the sponge, giving to it its irregularly hispid character. (6) Main; 

 consisting of a very loose and irregular reticulation of styli, often forming loose fibres 

 which run towards the surface and are crossed more or less at right angles by others. 



Sjncules. — (a) Megasclera ; of two kinds. (1) Smooth, stout styli (PI. XXVII. 

 fig 7), only slightly curved, measuring about 0'65 by 0"025 mm. (2) Tylota (PI. XXVII. 

 fig. *7a), with straight shaft and an oval head at each end ; the head is sometimes very 

 slightly spined at the top, where it may also be slightly flattened. Usually one end of the 

 spicule is a little larger than the other. Size about 0"3 by O'OOS mm. {h) Microsclera; 

 one kind only present ; viz., large, tridentate isochelse (PI. XXVII. fig. 7b), with a 

 slightly curved shaft which is markedly expanded laterally towards each end ; length 

 about 0"08 mm. These are plentiful in the dermal membrane and also occur scattered 

 through the deeper tissues of the sponge. 



Perhaps the most striking features of this sponge are the great size of the pores and 

 their arrangement in definite pore-areas. These strongly resemble the corresponding 

 structures in Halichondria forcipis, Bk. , as described and figured by Carter.^ The 

 species difi"ers markedly from the two preceding ones in the absence of sigmata. 



Its spiculation agrees in hind with that of Crihrella hainigera, Schmidt,^ but in 

 that species the styli tend to develop heads, and the sj^icules throughout are merely the 

 miniatures of those of this species. 



Zoca%.— Station 306a, January 2, 1876 ; lat. 48° 27' S., long. 74° 30' W.; ofi" the 

 south-west coast of Patagonia ; depth, 345 fathoms ; bottom, blue mud ; bottom 

 temperature, 46°. One specimen. 



Myxillafusca, Eidley and Dendy (PI. XXVII. figs. 11, 11a, llh). 



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



Sponge massive, amorphous, the largest specimen about 19 mm. in greatest 

 diameter. Colour in spirit darkish brown. Texture fairly firm and elastic, but rather 

 coarse. Surface uneven, in places minutely hispid. Dermal membrane adhering firmly 

 to the underlying tissues ; thin, granular and pigmented, brown in colour but trans- 

 lucent. Pores apparently collected into pore-areas, wherein they reduce the dermal 



1 Ann and. Mag. Nat. Hist., ser. 4, vol. xiv. p. 246, pi. xiv. fig. 29, a, 

 ' Spong. Adriat. Meer., p. 70, pi. vi. fig. 13. 



