354 Dr. G. J. Hinde on a true Leuconid Galcis^onge 



there are indications of the larger apertures of excurrent 

 canals. As, however, the intermediate spaces in the spicules 

 of the wall are generally tilled with an extremely fine pow- 

 dery matrix, the courses of the canals, even on the supposition 

 that they were similar to those of existing Leucones of corre- 

 sponding dimensions, would be to a great extent unrecog- 

 nizable. 



The examples of this species occur detached and free in a 

 decayed rusty rock, mingled with sand and oolitic grains and 

 broken-up fragments of Crinoidea or other Echinodcrms. 

 Many retain their outer form as perfectly as any specimen of 

 Grantia which might be met with on our coasts at the present 

 day ; others have been fractured, and small portions of their 

 wall are found separately. The sand-grains &c. now attached 

 to the bases of some of the specimens are probably the original 

 materials on which the sponge fixed itself during its growth. 

 Not only do these sponges retain their outer form, but the 

 structure of their walls with their loosely arranged interfelted 

 spicules is apparently undisturbed. As already mentioned, 

 the sponges are now infilled with a powdery rusty matrix, 

 much in the same way as recent specimens will get charged 

 with muddy sediment ; and this matrix can be partially re- 

 moved by gentle washing, leaving the loose spicular wall 

 exposed nearly in its pristine condition (fig. 6). By breaking 

 otf a fragment of the sponge and still further treating it with 

 water or with a drop or two of spirits of wine, aided by gently 

 touching with a needle or camel's-hair brush, the spicular 

 felt-work becomes disentangled, and its individual constituents 

 separated from each other as readily as those of recent Calci- 

 spouges by the action of caustic potash. In reality the struc- 

 ture of these fossil sponges has been preserved almost unaltered 

 and uninjured, in spite of the fact that the spicules of which 

 they consist are exceedingly slender, fragile, and minute, and 

 that they are only loosely and irregularly intermingled 

 together. 



As regards brittleness, however, the spicules of the Lias 

 sponges now fracture much more readily than those of existing 

 analogues, and it is exceptional to find perfect forms in micro- 

 scopic mountings from them. Under tlie microscope the 

 spicules vary but slightly in appearance from recent forms j 

 their lustre is hardly so brilliant, but their surfaces are equally 

 smooth and even, and show no traces of erosion. In polarized 

 light they behave the same as recent Calcisponge spicules. I 

 have not noticed any traces of axial canals ; but even in recent 

 sjjicules of similar dimensions it is very rarely that the canals 

 can be distinguished. 



