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



Esperella fusca, Ridley and Dendy (PI. XIV. fig. 4 ; PI. XV. figs. 3, 3o, 15, 15a). 



1886. Esperella fusca, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 339. 



Sponge (PI. XIV. fig. 4) small, incipiently lobose, rounded, penetrated through and 

 through by the branches of some Alga. Greatest diameter rather under 25 mm. Colour 

 in spuit dark greyish-brown. Texture soft, resihent. Surface very slightly roughened 

 by the presence of the dermal skeleton reticulation, but not hispid; uneven, with rounded 

 elevations and depressions. Dermal membrane distinct, transparent. Oscula few, small, 

 with their margins produced into small elongated tubes. Pores few, small, scattered ; 

 diameter about 0'025 mm. 



Skeleton. — (a) Dermal; composed of two layers: — (1) an upper layer, consisting of 

 a rather close, irregular spicular reticulation, in which several spicules often lie side 

 by side forming rudimentary fibres ; and (2) a lower layer, consisting of a reticulation 

 of fairly stout, compact, spiculo-fibre, with rounded or polygonal meshes. (&) Main; 

 composed of loose, branching spiculo-fibre. The main fibres do not, as in so many 

 Esiyerellw, break up into distinct divergent brushes of spicules on approaching the surface, 

 hence the surface is not hispid. 



Spicules. — {a) Megasclera; of one kind only, viz., tylostyli (PL XV. figs. 3, 3a), 

 often curved, with distinct oval heads and usually much blunted at the apex ; size 

 about 0'455 by 0'0126 mm. (h) Microsclera; (l) a few palmate anisochelse (PL XV. 

 figs. 15, 15a), of the usual Esiierella type (sometimes in rosettes?); length about 

 0'063 mm. ; numerous smaller ones also occur, probably young forms of the larger, 

 (2) Small, slender sigmata, usually contort, length about 0"044 mm. (3) Trichodragmata, 

 forming small, compact, oblong bundles, measuring about 0'03 by 0*063 mm, ; especially 

 abundant in the dermal layer. 



This sponge is remarkable for the ease with which the flagellated chambers 

 can be made out. If a fragment, without any staining, be teased up in a drop of 

 Canada balsam, the flagellated chambers are separated out in enormous numbers from 

 the surrounding matrix, and appear under a low power of the microscope as spherical 

 or oval bodies, composed of aggregations of large granules. Further details concerning 

 them will be found in the Introduction. They are about 0'03 mm. in diameter. 



Locality. — Ofi'Bahia; depth, 17 fathoms. Four specimens. 



Esperella arenicola, Ridley and Dendy (PL XV. figs. 4, 4a ; PL XVI. fig. 8). 



1886. Esperdla arenicola, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol xvui. 



p. 339. 



Sponge (PL XVI. fig. 8) massive, flat, cake-like. Length of largest piece 175 mm. ; 

 breadth 81 mm. ; thickness 16 mm. Colour in spu-it light brown. Texture fragile, 



