Marine Sponges from Japan. 393 



The grouping of the heads of the clavulce around the knob 

 which represents the aborted outer ray of the dermal sexra- 

 diate, together with the lattice- work itself formed by these 

 spicules (fig. 11), recalls to mind Dr. J. Millar's discovery of 

 this kind of arrangement in the dermal structure of Eupleciella 

 cucumer, faithfully represented from one of Dr. Millar's own 

 preparations which he gave to Dr. Bowerbank (Proc. Zool. 

 Soc. 1875, p. 503, pi. lvi.) ; only that here it is the rosette 

 which is brought to the surface and projected upon the point 

 of the outer ray of the dermal sexradiate, which, instead 

 of being aborted, as in Farrea occa, is fully developed. 

 See also Prof. Schulze's representations of this ( l Chal- 

 lenger ' Reports, Sponges, Rexactinellidse, Eupleciella asper- 

 gillum, pi. A. figs. 3, 4, and 5). Lastly, there appears to 

 have been something like this in the fossil species Callodic- 

 tyon angustatum, Hinde, and Porochonia simplex, T. Smith, 

 if not also in the two foregoing species (H hide's Catalogue 

 Foss. Sponges in the Brit. Museum, 1883, pi. xxx. figs. 4 b 

 and 5 b) . 



As regards the general structure of Farrea occa there can 

 be no doubt that it belongs to the family of Euritida3, whose 

 tubo-branched structure is faithfully represented in my illus- 

 tration of Eurete farreopsis ('Annals/ 1877, vol. xix. pi. ix. 

 fig. 1), which is taken from a photograph of the natural size 

 of the specimen, but in such a position as to show the open- 

 ings and structure of the tubo-branches, through which the 

 basal structure or stem is necessarily concealed from view. 

 Etymologically, the term " Eurete," par excellence, applies 

 to the wall of Farrea occa ; but its consisting only of a single 

 skeletal layer together with the absence of a scopuline spicule 

 (Besengabel) and the presence of the clavula, causes it to differ. 



Again, the measurements of the spicules in the vitreous 

 Hexactinellida are so variable that it is almost impossible to 

 arrive at any that are satisfactory, on account of the addition 

 of the siliceous slime to their exterior which is continually 

 going on preparatory to their becoming incorporated with the 

 skeletal fibre, after the manner of the spicules in the Keratose 

 sponges ; but whereas in the latter the contrast immediately 

 renders them recognizable, the vitreous fibre, being of the 

 same composition as the spicule, defies all attempt at separa- 

 tion in the recent specimen. 



Lastly, the siliceous slime leads to the formation of skeletal 

 fibre, which has its own specific character, as in the present 

 species, viz. Farrea occa, in which it is smooth, while in the 

 following species, viz. FeripkrageVa Elisce and Hexactinella 

 ventilabrum, it is spiniferous. 



