32 Mr. H. J. Carter on the 



nized by the casts of its borings alone (No. 8, vol. iii. pp. 

 305, 306) ; while his Tetractinellidae, which do not concern 

 us so much here, hardly fare a bit better. Again ? in the 

 British-Museum collection the same thing is repeated. Nothing 

 meets one's eye to correspond with the great number of ex- 

 isting Monactinellid sponges in the Zoological Department. 



If we are not to infer the original nature of fossil sponges 

 from the resemblance of their spicules to those of existing 

 ones (that is, the presence of the peculiarly formed tri- and 

 quadriradiates to indicate a calcareous, and that of a monacti- 

 nellid spicule, such as in Pharetrospongia Strahani, to betoken 

 a siliceous spicule, like that of a Renierid among my Holorha- 

 phidota), we must fall back upon the mineral composition ; and 

 we have seen how misleading this may be. It is true that a 

 calcareous spicule may remain calcareous under the influence 

 of a calcareous lye ; but this may not be the case with a sili- 

 ceous one. Witness the calcareous condition of the Hexacti- 

 nellid Acanthospongia Smithii, and, still more to the point, 

 the " pinlike spicule " in Mr. HolUs specimen of Verticillites 

 (see u P.S."). Again, if we confine all the fossil sponges to 

 the Hexactinellida, Lithistida, and Calcarea, together with a 

 few Pachytragid and Pachastrellid species, what become of the 

 fossil representatives of the great body of existing monactinellid 

 sponges to which I have alluded ? Are we prepared to even 

 conjecture that they are all recent introductions, when we find 

 some of their spicular forms already so far back as the Carbo- 

 niferous period (No. 6, vol. i. pi. ix. fig. 19, pi. x. fig. 5 ; and 

 No. 10, vol. iii. pi. xxi. fig. 11, also in No. 12, vol. vi. pi. xiv. 



fig. 14) at least ? 



I think not, and therefore, for the present, prefer consider- 

 ing such fossil sponges as Pharetrospongia Strahani, although 

 at present calcareous, to have originally been siliceous and 

 allied to the existing Monactinellida, to which I have alluded, 

 rather than to the Calcispongias, among which Zittel has 

 placed them. 



Returning to the latter for a moment, I cannot help observ- 

 ing that the important confirmation supplied by Dr. Hinde 

 respecting the kind of spicules of which that unique little 

 form Verticillites was composed, cannot be overrated ; nor can 

 his. discovery of the peculiar kind of spiculation in Sestro- 

 stomella, together with the presence of the pitchfork-like 

 spicules (two-pronged) identified with those of existing species, 

 as before mentioned, be considered otherwise than as opening 

 up an entirely new although fossil character, which must 

 become most useful in classification. 



To the sheathed form of this spiculation I have already 



