" Farringdon {Coral-Rag) Sponges." 435 



p. 153. fig. 68). My Farringdon specimen of Elasmostoma is 

 very perfect, but in form cupellate with a chink on one side 

 and still open below, evidencing what I have elsewhere stated 

 respecting the funnel-shaped sponges, viz. that they begin in 

 the form of a fan, and then curving round, the opposite borders 

 unite to such an extent as finally to convert the fan into a 

 vase-shaped sponge. 



Now no one can confound the triradiate spicule of a Calci- 

 sponge with the tetracladiate one of a Lithistid when both 

 are clearly exposed ; but in these obscure indications which 

 can only be dimly seen in the calcified fibre of the Farringdon 

 sponges when it is ground down to a thinness which must 

 take off one or more of their branches, we are as likely to find 

 an apparent identification with one as with the other. Hence, 

 perhaps, the value of my communication to Prof. Zittel that 

 his slice of Peronella multidigitata presented triradiates which 

 could only be identified with those of the recent Calcispongise ; 

 and hence the dubiousness which attended the " results " of 

 my grinding-down of the slices of the Farringdon sponges 

 above mentioned. 



Professor Zittel's " Studies on Fossil Sponges," to which I 

 have already alluded, are to me beyond all praise ; they form 

 quite an epoch in the palreontological history of the Spongida, 

 especially as regards the Hexactinellidaj and Lithistidas ; but 

 when we come to his Monactinellidas and Tetractinellidce his 

 material, if not also the time that he could spare for this 

 part of his ' Handbuch der Paliiontologie,' appears to have 

 been pretty well exhausted ; for while, in the translations 

 (' Annals/ I. c), about 128 pages are occupied by the 

 Ilexactinellidas and Lithistidae, only 14 are given to the 

 Monactinellida3 and Tetractinellida?, with 43 for his fossil 

 Calcispongiffi. 



Thus, considering that the Monactinellidaa and Tetracti- 

 nellida; are incomparably more numerous at the present day 

 than the Hexactinellidre and Lithistidse, it follows that either 

 the former were far less plentiful in palajontological times than 

 they are now, or that very few specimens have come to Prof. 

 Zittel's hands in a fossilized condition ; while the chances of 

 the Calcispongiaj not being preserved, for the reasons I have 

 heretofore stated, make it questionable whether Zittel has not 

 termed " Calcispongias " many which ought to be among the 

 siliceous sponges. 



Again, I agree with Mr. Sollas (Ann. 1878, vol. ii. p. 3G1) 

 that, if " well cleansed by caustic potash," or, indeed, by fresh 

 water, so as to extract the salt (chloride of sodium), the 

 spicules of a Calcisponge might be preserved in balsam for 



31* 



