Hexactinellidge and Lithistidse. 449 



Besides the specimens mentioned, there are two other thin 

 flat portions, each of which is about an inch square and 4* inch 

 thick, which, presenting no visible curvature, may have belonged 

 to infundibuliform heads of much larger dimensions than those 

 above given. It is not improbable too, from the extreme thin- 

 ness of the margin of the expansion of the more perfect speci- 

 mens, that, if the heads in them respectively had been entire, 

 their diameter would also have been greater. The flat portions 

 must have been broken off from living specimens, as they are 

 covered with dry sarcode abundantly charged with the form 

 of rosette above mentioned. 



This differs from Farrea occa : — 1st, in the addition to the 

 single lattice-like layer of which Farrea occa is composed, of 

 a much larger, obliquely anastomosing, branched, vitreous 

 fibre, apparently originating, both outside and in, from the 

 bottom of the funnel-shaped expansion where it is thickest ; 

 2nd, in this fibre being charged with the minute sexradiate 

 spicules of the species, confusedly imbedded, entirely or par- 

 tially (that is, in various degrees), within its substance ; 3rd, in 

 these sexradiates being much smaller than those singly and 

 regularly arranged in what appears to be the basework or 

 original lattice-like fibre of a Farrea occa. In short, the 

 branched anastomosing fibre charged with the minute sexradiate 

 spicules appears to be a secondary formation, which has run 

 over a rectangular fibre vertically, so that it cuts the transverse 

 bars of the latter, although amalgamating with them here and 

 there at right angles. 



Spicules of the Apkrocazlistid^:, Aulodictyon, and 

 Farrea facunda. 



We now come to the description of the spicules respectively 

 of the Aphrocallistidos and Aulodictyon Woodwardii in their 

 living state, together with a species of Farrea described by 

 Schmidt as F. facunda (fecunda?), with all of which it will be 

 found necessary that we should become acquainted before we 

 can make out any thing of those in the deciduous skeletons. 



Aphrocallistidae. 



Apkrocalltstes beatrix, Gray, and A. Bocagez, Wright. 



These two sponges have been excellently described and illus- 

 trated by the naturalists respectively who named and brought 

 them into notice. But only generally. The detail of their 

 spicules has not been sufficiently given ; and as it is neces- 

 sary that this should be minutely done, in connexion with illus- 

 trations, before their histories respectively can be considered 



31* 



