124 Mr. H.J. Carter on Fossil Sjjonge-sjncules of 



Coralliospongia3. Such fragments are so abundant and so in- 

 finite in the variety of their forms in this deposit, that it has 

 been a matter of difiiculty to make any selection that could 

 give even their general character. 



Most of them have small spicules, fragmental or entire, ad- 

 hering to them, as in figs. 19 and 24, which are drawn upon 

 the same scale as the rest of the figures (indeed it should be 

 remembered that not only all the figures except 7, 8, and 9, 

 but every thing connected with them, are drawn upon the same 

 scale in these representations). Such small spicules, as has 

 been heretofore explained, need not have had any previous 

 existence in the sponges from which the fragments to which 

 they now adhere belonged. 



Again^ as there is also a great abundance of the globular 

 crystalloids (little siliceous balls) of the Geodidfe in the de- 

 posit, many of these also, as rejiresented in figs. 20 and 24, 

 adhere firmly to the larger spicules of all kinds ; these, in 

 like manner, need not have had any connexion before the 

 deposit took place with the spicules to which they are now 

 attached. I particularly mention this, because the occurrence 

 has often led me to the opposite conclusion, which subsequent 

 reflection has thus corrected. 



Figs. 25, 26, and 28 represent instances where the small 

 spicules did appear to have been incorporated with the silici- 

 ficd fibre from the beginning, as seen especially in the AjyJiro- 

 callistes. Indeed the imbedding of the spicules in the silici- 

 fied fibre of the Coralliospongiaa, while it has its analogue in 

 the entire enclosure of them in the living fibre of the Chalineaj, 

 or in the insertion of their blunt ends only, as in that of the 

 Oplitospongiaj, Bk., seems, in the Coralliospongiffi, to have 

 been as present and necessary for the support of their delicate 

 spicular structure in the more shallow tidal seas in which they 

 live and have lived as it is absent and unnecessary in the 

 flimsy spicular structure of the deep-sea sponges, which, like 

 Ashonema sefubalense, Kent, attains " upwards of three feet in 

 diameter " in the quiet valleys of the Atlantic Ocean (Monthly 

 Microscop. Journ., Nov. 1870, p. 245, pi. Ixiv.). 



Fig. 29 represents a piece of silicified fibre with holes in 

 it (a) — a very common occurrence, as may be supposed, in the 

 Coralliospongite. 



Following the numbers, we now come to the spicules of the 

 Pachytragije, whose heads, where the shafts have been broken 

 off entirely, and where fragments of them still remain, are re- 

 presented in Plates IX. and X. respectively ; and here we 

 meet with the difficulty of determining, not only how many of 

 those in PL IX., where the heads are without shafts, belonged 



