PART’ IT. 
SPONGES OF THE PALAOZOIC GROUP. 
PRELIMINARY REMARKS. 
Up to a comparatively recent period so few genuine fossil Sponges were known 
from the older stratified rocks of the British area, that it would have been super- 
fluous to devote a separate portion of a Monograph especially to their consideration. 
Even now the number of species is very limited in comparison with those 
from the Mesozoic strata, and their state of preservation is very unfavorable ; 
but recent discoveries show that Sponges as a group flourished to such an extent 
in certain epochs of the Paleozoic era as to form by their remains massive beds 
of rock of considerable thickness, and, measured by this scale, they were then 
more numerous than at any subsequent geological period. 
In view of this enormous development of Sponge-life, it is reasonable to 
suppose that the small number of species known hitherto falls far short of those 
which then existed. In no group of organisms with structures capable of 
preservation have the influences of fossilisation acted with more destructive effect 
than upon fossil Sponges; at all events, on those in the Paleozoic rocks ; for 
thick beds occur built up almost exclusively of their remains, and yet not a single 
entire individual has been preserved in them! Their elaborate skeletal tissues 
have been altogether disintegrated, and only their minute, microscopical, spicular 
elements, heterogeneously mingled and cemented together into hard rock, remain 
for examination. 
Under more favorable conditions entire Sponges and fragmentary portions 
of the connected skeleton are occasionally met with, but at the best the materials 
for the classification and description of these organisms are very imperfect and 
unsatisfactory, and such as would be rejected by the student of the hving forms 
as altogether insufficient to furnish generic or specific characters. But since more 
perfect materials are not available, the paleontologist is compelled to make the 
most of those which are at his disposal. It will readily be conceded that the 
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