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



to make a genus for the other grouj) of species, viz., those with smooth surface, but 

 experience has shown that it will be advisable to leave this question to some naturalist 

 who has more opportunity for studying a large series of forms. Hence we include both 

 groups under the name Pachychalina. 



Pachyclialina fragilis, Ridley and Dendy (PL IV. figs. 2, 2a). 



1886. Dasychalina fragilis, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, voL xviii. p. 330. 



Sponge (PI. TV. figs. 2, 2a) irregularly ramose, subcylindrical, aculeated ; branches 

 averaging about 1 8 mm. in diameter. Colour in spirit light greyish- or brownish -yellow. 

 Texture hard and brittle. Surface very uneven, covered with sharp aculeations ; 

 delicately striate, with the strias radiating from the summits of the aculeations.^ 

 Oscula large and scattered, but almost entirely confined to one side of each branch ; 

 about 4 mm. in diameter. 



Skeleton. — (a) Dermal ; an irregular reticulation of individual spicules and spiculo- 

 fibre, backed up behind by a much coarser reticulation of much stouter spiculo-fibre, 

 the nodes of which form the apices of the surface aculeations. (h) Main ; an irregular 

 reticulation of very stout, compact spiculo-fibre and abundantly scattered spicules ; the 

 fibres are about 0"35 mm. thick, and the main fibres terminate on the surface at the 

 summits of the aculeations. There is no doubt a good deal of spongin present uniting 

 the spicules, but it is difficult to make out, and does not form a distinct sheath around 

 the fibres as in typical Chalininse. The fibre resembles that of Petrosia. 



Spicules. — Oxea, very large for a Chalinine sponge ; rather stout, slightly curved, 

 suddenly and more or less bluntly pointed ; size about 0"42 by 0'02 mm. 



Taken by itself this species might have been described as a Petrosia, characterised 

 by the aculeations on the surface, but it forms the first of a series of allied forms which 

 seem to lead up from the Eenierinse to more typical species of Paehychalina and 

 Spinosella. 



Locality. — Station 208, January 17, 1875; lat. 11° 37' N., long. 123° 31' E.; 

 Philippine Islands; depth, 18 fathoms; bottom, blue mud. Several large pieces. 



Pachychalina melior, Ridley and Dendy (PI. IV. fig. 1). 



1886. Dasychalina melior, Kidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 330. 



Sponge (PL IV. fig. 1) irregularly branched; branches subcylindrical or angular, 

 coarsely aculeated ; aculeations less abundant and weU marked than in Pachychalina 

 fragilis. Average diameter of branches about 12 mm. Colour in spirit greyish- or 

 brownish-yellow. Texture compressible, fibrous, but rather hard. Surface uneven, 



' In one small specimen only this striation of the surface is not visible. 



