TETKAXONIDA. 19 



The choanosomal skeleton is formed of fibres radiating upwards from the base to 

 the periphery, and spreading out in the upper third of their course ; they do not pene- 

 trate the cortex. 



Spicules. Choanosomal tyles of the radiating fibres, 1120 x 20//,, straight, 

 fusiform, attenuating gradually to a sharp point; head long, oval, 20 /x long, 17 ju, 

 broad. 



Tyles scattered between the radial fibres, varying in length from .370 to 600 fi, 

 slightly curved. 



Exotyles in form of spherotyles, 760 /a long and 40 [x in diameter at the broad 

 distal end, which is elavate, and with a granulated surface ; the heads at the proximal 

 end (in the interior of the sponge) are 15 /a in diameter. 



The cortical tyles (XIII. 11), 218 x 12-5 yn, are slender, tapering, curved, and 

 with small oval heads and a thin neck ; there is a shorter, straighter variety of cortical 

 tyle (XIII. 12, 12a) with a relatively thicker neck, and abruptly pointed. 



Although there is some uncertainty as to the actual size of the spicules in the 

 specimen described by Vosmaer, yet the relative proportions and characters of these 

 spicules are very similar in the Arctic and Antarctic specimens. The Arctic specimen 

 was globular and 2 cm. in diameter. 



Topsent mentions Radiella schoenus Sollas, as a synonym of Vosmaer's species. 

 Sollas gives the only names without generic or specific definition. 



The specimen was obtained from Winter Quarters, oft' Flagon Point, 10-20 fms. 

 It has also been found at Lat. 72° 14' 8" N., Long. 22° 30' 9" E., 165 fms., Vosmaer, 

 Willem Barents Expedition. 



Family Suberitidae, Schmidt. 

 SuBERiTES MICROSTOMUS vav. stellatus. 

 (Plate XV., figs. 8-13.) 



Suberites microstomus Ridley aud Dendy (15. p. 199). 



There are four small specimens in the form of smooth, pale-coloured, whitish 

 rounded masses, smooth to the eye but slightly rough to the touch, encrusting the 

 stems of branching Polyzoa ; the largest is about 4"5 cm. long and 2"5 cm. broad, aud 

 forms a nodulated mass on the branch of the Polyzoon. 



There are two or three minute conical pointed oscular papillae about 1 mm. high. 

 The pores occur in stellate areas among the cortical tyles which occupy the rest of 

 the surface. The skeleton is composed of radiating fibres and of a dense cortical layer 

 of vertical or oblique tyles. 



Spicules. Megascleres. Large straight fusiform tyles with an oval head, 

 gradually attenuating to a sharp point, 1130 x 24 /a. The head (XV. 9a) is usually 

 sub-tylote or even stylote, and has a sub-terminal oval swelling 13/x in diameter. The 

 cortical tyles vary considerably, the figures showing three kinds. The largest 500 x 30 /i 



