460 Mr. II. J. Carter on tlie 



Farrea occa a scopuline spicule with pointed rays was found, 

 like that figured by Schmidt in his Farrea facunda [I.e.). 

 These specimens were also mounted in Canada balsam and 

 delineated, as the illustrations will show (PI. XVI. figs. 6, h, 

 &7,b). ^ 



Lastly, in many instances in the fibre of Farrea occa the 

 capitate end of a largish spicule was observed (fig. 7, c) , which 

 I see appears in one of Schmidt's fossil illustrations {op. cit. 

 pi. ii. fig. 18) as an arm of a sexradiate spicule. Of this 

 form I can state, as I know, nothing further. 



I had hoped, by finding this specimen of Farrea enve- 

 loped in the Gummina, that I might also find some of its 

 isolated spicules within the tube ; but, with the exception of 

 four sexradiates of the form no. 3 under Aphrocallistes Bocageij 

 viz. that with the feather-like spined arm (PI. XV. fig. 9), I 

 could not, even after repeated searching, see any thing of the 

 kind. 



Whether or not these spicules did belong to Farrea occa I 

 am unable to state, since together with the Farrea were in- 

 cluded in the Gummina some fragments of Aphrocallistes 

 Bocagei^ one of which, as wnll be seen by the illustration, bears 

 a mould of the sexradiate spicule with feather-like arm just 

 mentioned. That such spicules are involved in the vitreous 

 skeleton of this sponge has been already shown by the em- 

 bryonic specimen mentioned at p. 452. 



In the " stick-like " fragment among Mr. Gassiot's speci- 

 mens, also above noticed, which looks like the solid stem of 

 Farrea iTrfundihuliformis^ the absorbing process has gone on 

 to such an extent internally as to destroy all forms of the sex- 

 radiate spicules on which the vitreous fibre of which it is 

 composed was built, and externally to such a degree as to 

 round off and diminish in size every spine and original pro- 

 jection of this fibre ; so that it now presents the white appear- 

 ance and form of a substance that is disappearing under the 

 dissolving influence of water. Such is another instance of the 

 way in which the fibre of the hexactinellid sponges may pass 

 into dissolution. 



We learn from the foregoing, then : — 



1st. That the vitreous structure of the Hexactinellidse is 

 built upon a network of their spicules, as ])roved by the ex- 

 amination of the embryonic forms of Aphrocallistes Bocagei^ 

 in one of which (viz. that -^V of an- inch in diameter) the 

 process of vitrification has not commenced, while in the other 

 (-i-\ of an inch in diameter), although incomplete, it has already 

 made considerable progress ; that after the spicules have become 

 enveloped in the vitrification their forms disappear ; and that. 



