436 On the so-called u Farringdon {Coral-Rag) Sponges. 11 



an indefinite period ; but I do not think this cleansing is likely 

 to occur in the sea, and therefore that the rapid destruction of 

 these sponges, which appears to me to be owing to the pre- 

 sence of sea-salt in the spicules, must be opposed to their ever 

 being found in a fossilized condition. 



But I cannot agree with Zittel in considering Pharetro* 

 spongia Strahani a Calcisponge ; for, in the first place, from 

 what has been above stated, there is no reason to assume that 

 calcareous material was its original composition ; and, secondly, 

 the acerate spicule is in form as peculiarly that of a Renierid 

 as it is not that of a Calcisponge. 



With reference to my having also heretofore shown that 

 both Pachastrellid and Echinonematous sponges may possess 

 triradiate spicules (Ann. 1876, vol. xviii. pi. xiv. and 1879, 

 vol. iii. pi. xxvii.), I do not think that the latter can be 

 confounded with the triradiates in the fossil Peronella multi- 

 Jida, nor arc they like those of P. eylindrica, although those 

 of P. eylindrica might be confounded with the spicules of a 

 Pachastrellid, e. g. Dercitus niger, Gray (Ann. 1871, vol. viii. 

 pi. iv. fig. S), — Batta-sbya Bucklandi, Bowerbank (Mon. Brit. 

 Spongiada3, vol. iii. pi. xcii. fig. 8, 1874) : the spicules in the 

 latter illustration are particularly like those of P. eylindrica. 



Lastly, I have of late been examining the cherry, flint-like 

 detrital remains of the Upper Greensand (Cenomanien) 

 which are now strewn over the surface of the New Hed Sand- 

 stone of this neighbourhood in vast abundance, from their 

 consisting of the once continuous and superincumbent strata 

 of these parts, which, judging from their composition, were 

 formed of the subtle material of a deep ocean- bed, in which 

 all kinds of sponges, but especially the Hexactinellida and 

 Lithistida, seem from their abundance to have attained their 

 maximum of development ; yet while these are imbedded, for 

 the most part, in large fragments in this more subtle material, 

 which has now passed into a translucent, flint-like, siliceous 

 matrix, equally abounding in isolated spicules of every kind 

 of siliceous sponge, I have never seen a form among the 

 latter that I could identify with a triradiate, quadriradiate, 

 linear, or any other kind of spicule of a Calcisponge, although 

 often a Lithistid with weathered-out white fibre like that of 

 the Farringdon sponges but silicified. 



Furthermore, a few days ago a fragment of this detritus was 

 brought to me, out of which I extricated the digital process of 

 a fossilized sponge about two and a half inches long and three 

 eighths of an inch thick, which by its fixed end had evidently 

 been attached to a larger branch, and at its free end is ob- 

 tusely round. Thus from its shape, together with the pre- 



