> 





so-called "Farringdon Sponges." 35 



from a Calcisponge, which most probably was the Protosycon 

 itself. Verticillites was also a Sycone, and Peronella dumosa 

 a Leucone. 







Before concluding these "observations," it might be ai 

 well to direct our attention for a few moments to the structure 

 of the fibre in the fossil Calcispongise. Thus in Sestrosto- 

 mella and Scyphia cylindrica the large axial spicules are 

 ensheathed in a variable number of layers, which appear to be 

 more or less concentric and to have originated in the spicule 

 itself, thus causing the fibre to resemble, as before stated, that 

 of the vitreous Hexactinellida, while the pitchfork-like spicules 

 and smaller triradiates being in the midst of this fibre recalls 

 to mind what I long since pointed out in the fibre of Aphro- 

 callistes Bocagei ( 6 Annals,' 1873, vol. xii. pi. xvi. figs. 1, 

 &c.) , wherein an analogous structure is witnessed *. On the 

 other hand, in Verticillites &c. there is no investment of this 

 kind, but one of crystalline calcite, which seems to have arisen 

 from the presence of a calcifying lye, probably produced by a 

 partial dissolution of the calcispicules themselves ; for this is 

 the condition in many instances, where hardly enough of the 

 triradiates remain to verify their existence. 



P.S. Since writing the above I have had the pleasure to 

 receive from Dr. Harvey B. Holl, of Claines, near Worcester, 

 four slides of Verticillites anastomans^ showing that the reticu- 

 lated structure of this little fossil is formed of triradiate spicules 

 arranged around polygonal interstices, precisely like and almost 

 identical in size with those of a specimen of Grantia compressa 

 now before me, and exceedingly well shown in Dr. Bower- 

 bank's illustration (No. 1, vol. i. pi. xxi. fig. 313). This, 

 then, besides confirming Dr. Hinde's discovery of a similar 

 structure in his Verticillites D 1 Orbignyi (No. 14, vol. x. p. 192), 

 shows that a true Calcisponge like those of existing species, 

 although extinct in general form, may, as Zittel was the first 

 to proclaim, be fossilized. Whatever doubts, therefore, that I 

 have before expressed respecting this must now be repudiated. 



But Mr. HolPs preparations show more than this, and were 

 kindly forwarded to me to point out that the fibre in Verticil- 



* Can it be possible after all, that this concentric lamination is mine- 

 ral and not organic — that is, that the calcareous layers are but a repro- 

 duction inform of the original spicules, which, during fossilization, have 

 become dissolved and furnished this solution for the new structure (as 

 often seen in the chalcedonization of the vitreous sponges, or as agatoid 

 layers round a grain of extraneous matter ? The examination of another 

 slice of my specimen of Sestrostomelkt from the Jura strongly inclines me 

 to this view. 



3* 



