272 TT. J. Sollas — On Greensand Foymmini/era and Sponges. 



ever, with Lis uniform kindness, placed at my disposal a large 

 number of slides, on which are founded my succeeding observations. 



The parts of a sponge which are most likely to be preserved are its 

 siliceous spicules, and in most of the Coprolites of the formation 

 spicules of one kind or another are to be found in greater or less 

 abundance; a few simple needle-shaped spicules may generally be met 

 with in any ordinary nodule, but in some particular forms they are 

 especially numerous. Khabdospongia has furnished some very fine 

 examples ; but, in the number and variety of their contained spicules 

 PolyacantJia Etlieridgii and Acanthophora Hartogii far surpass all the 

 rest. In both of these species hexradiate, quadriradiate, triradiate, 

 and sinuous spicules are to be met with, and one of them is character- 

 ized especially by its porrecto- and recurvo-ternate forms. It is 

 important to notice that the sjDicules are not only of indisputable 

 sponge forms, but are sometimes also arranged in a manner which 

 seems to indicate, that they occur in situ, and were not waslied in 

 during fossilization. 



Yarious other bodies accompany the spicules in these sections, and 

 in solution. Little spherules ^-i-g-" a-d-o- " ^^® ^o^ uncommon, and 

 unless they are spicular in origin, it is difficult to conceive what 

 else they can be but sponge gemmules. In some sections Xanthidia 

 may be observed of the same species as those of the Chalk — X. 

 hirsiitum, X. ramosum, X. tuhiferum. Polycystina of various genera 

 also occur, and will shortly be described ; forms resembling Haliomma 

 may be noticed of somewhat common occurrence. 



It is important to notice, as deciding the siliceous nature of the 

 included spicules, that on dissolving the Coprolites in concentrated 

 hydrochloric acid, an insoluble residue remains, which contains the 

 spiculee of the organism, together with its included Polycystinee and 

 the XantMdia just enumerated. These may easily be observed 

 under the microscope by suspending the residue that contains them 

 in a little water, and placing a drop of this on an ordinary glass 

 slide. The XantMdia that may be present are really beautiful 

 objects ; floating in the water on the slide, they swim about freelyin 

 its currents, and catch with their claw-like processes at every little 

 obstacle in their way, as though they were really alive. 



Mr. Carter ' has observed that in certain subspherous sponges the 

 contractility succeeding death is often so great as almost to obliterate 

 all their canals. That the organisms which furnished the Coprolites 

 underwent great contraction after death is shown by the deep creases 

 with which they are generally marked, while their contraction after 

 fossilization is exhibited in quite a different manner by numerous 

 sharply defined cracks. In consequence of this contraction, we 

 should scarcely expect to find more than mere traces of canals now 

 preserved, and as a general rule we do not. There are, however, 

 some exceptional cases ; for sometimes lighter streaks are seen drift- 

 ing through the dark-brown Coprolite somewhat like the digitations 

 of a river in its delta ; and in single instances a vacant tube, circular 



1 A descriptive account of four subsplierous sponges, Arabian and British. J. H. 

 Carter, F.R.S., Ann. Mag, Nat. Hist., ser. 4, vol. iv., p. 1, 1869. 



