124 ]\Ir. n. J. Carter on Fossil Sponge-spicules of 



Coralliospongije. 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 difficulty 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 figm-es (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 Geodid^ in the de- 

 posit, many of these also, as represented 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 2<S represent instances where the small 

 spicules did appear to have been incorporated with the silici- 

 fied fibre from the beginning, as seen especially in the Aphro- 

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

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

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

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

 Oplitospongiai, Bk., seems, in the Coralliospongiaj, to have 

 been as present and necessary for the support of their delicate 

 spicular structure in the more shallow tidal seas in which tliey 

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

 flimsy spicular structm-e of the deep-sea sponges, which, like 

 Askonema setuhalense, 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 silicificd fibre with holes in 

 it [a] — a very common occun-ence, as may be supposed, in the 

 ' Coralliospongia3. 



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

 Pachytragias, Avhose heads, where the shafts have been broken 

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

 presented in Plates TX. and X. respectively ; and here Ave 

 meet Avith the difficulty of determining, not only Iioav many of 

 those in Pl. IX., Avhere the heads are Avithoutj^hafts, belonged 



