478 " THETIS " SCIENTIFIC RESULTS. 



Small isochelse C-013 mm. long. Both kinds of spicules are 

 fairly abundant. 



This species closely resembles Desmxacidon [Homoeodictya) 

 grandis, Ridley and Dendy,* but diifers in most of its internal 

 characters from the African species. 



DESMACIDON (^) ARENOSA, sp. nov. 



(Plate xliv., fig. 10.) 



Station 54. 



Sponge massive and bread-like in appearance, growing between 

 the roots of a seaweed {Ecklonia radiata, J. Ag.). The specimen 

 measures 70 mm. by 45 mm. and is about 30 mm. in height. 

 Surface covered with numerous small pores from 0'05 to 0*1 mm. 

 in diameter. The apparent oscula are irregularly scattered over 

 the sponge, and are usually 2 or 3 mm. across. A number of 

 larger apertures are also present, but these I regard as the work 

 of a boring Isopod. Texture firm but brittle. Colour when 

 fresh light terra-cotta ; in spirit or dried, yellowish-grey. 



Skeleton consisting of an intricate network of colourless fibres, 

 charged with sand grains and fragments of the spicules of other 

 sponges. The foreign materials in the fibres have a peculiar 

 feature, inasmuch as they are usually quadrate or slightly oblong 

 with sharp angles. The main fibres are about O'lSmm. or 0*2 

 mm in diameter, but here and there they are irregular, somewhat 

 nodose, and contracted or expanded according to the position in 

 the network. The secondaries and connecting fibres are very 

 indefinite and rarely exceed about 0"5 or 1 mm. in diameter. 



Megascleres : — probably absent ; one or two tylota were 

 observed, but they might be of foreign origin. 



Microscleres : — small isochelse, with the shaft straight or rarely 

 curved, and each end is provided with three or more teeth. Size 

 about 0"015 mm. When viewed from above the spicules appear 

 to be like those of lotrochota, but when .seen from the side the 

 teeth are evidently confined to one side of the axis. Desmacidon 

 chaliniformis, Carter, has microscleres of the same kind, but 

 they are somewhat smaller, and the horny matter of the fibres is 

 much more abundant. 



* Ridley and Dendy— Chall. Rep., Zool., xx., 1887, p. Ill, pi. xxii. 

 pi. xxix., figs. 7-7«. 



