248 Mr. W. J. Sollas on the 



the slender porrecto- and recurvo-ternate spicules (PL XI. 

 figs. 8, 9, and 16), as these are not completely represented 

 in Bowerbank's illustrations. In addition to the cylindro- 

 stellates mentioned by Bowerbank there are also present in 

 the mark a number of sharp-rayed forms, of which an instance 

 is represented in PI. XI. fig. 20. The cylindro-stellates of the 

 mark often attain a much larger size than those of the cortex, 

 which are exceedingly minute. 



The arrangement of the spicules has also been excellently 

 described by Bowerbank, so that I need now only call atten- 

 tion to the distribution of the stellates. The cylindro-stellates 

 are confined to the rind and the mark immediately surround- 

 ing the crypts, the sharp-pointed forms commence immediately 

 below the crypts, and are found throughout the rest of the 

 mark. They never occur in the rind. This distribution is 

 identical with that existing in Stelletta Normam, and probably 

 in most Pachytragous sponges possessing two varieties of 

 stellates. 



The Canal-system. — The single oscule opens into a cylin- 

 drical tube with a rounded termination (PI. X. fig. 1) ; it is 

 0'15 inch long and 0*1 inch wide ; its walls are smooth, but 

 rendered finely hispid by the projecting ends of small acerate 

 spicules, which cannot be seen with the naked eye. Ending 

 against the apparently imperforate walls of this tube, two canals 

 are seen in a transverse section of the sponge ; they are 

 0*1 inch wide, and descend from the oscular tube in a curved 

 direction more or less concentric with the outer surface of the 

 sponge. Although only these two tubes are shown in a single 

 transverse section, there can be no doubt that others exist and 

 Avould be revealed by fresh sections taken in different direc- 

 tions. The interior of these large excurrent tubes or main 

 trunks of the excurrent system (for such they are) has a smooth 

 glistening surface, which is concentrically striated by fine 

 circular ridges and furrows, reminding one in general appear- 

 ance of the " valvulee conniventes " of the small intestine, 

 though of course they are of very diminutive size (PI. X. 

 fig. 2, r). Similar folds, but possibly not quite so regular, 

 exist in Mr. Carter's sponge Axos spw^oculum, and have 

 suggested the same comparison to him (Ann. & Mag. Nat. 

 Hist. ser. 5, vol. iii. pi. xxv. figs. 4, 5, p. 287). A number 

 of sharply defined circular openings are seen in the walls of 

 the excurrent trunks, the commencement of secondary canals 

 which proceed from them and branch repeatedly in the sub- 

 stance of the sponge. 



Under a low-power magnification and by reflected light the 

 oscular tube exhibits two or three small circular openings, 



