2 BRITISH FOSSIL SPONGES. 
‘Studien ueber fossile Spongien’ this principle has been recognised and acted on, 
and the status of fossil Sponges is no longer one of reproach and contempt. The 
impetus thus given to the study of these fossils is well shown by the various works 
on them which have since appeared in different countries, in which they are 
classified according to the minute characters of the spicular components of their 
skeletons, and the descriptions in the present work will be primarily founded on these 
features. 
As preliminary to the description of the British forms I have thought it desirable 
to give a list of the principal works and papers treating of fossil Sponges generally, 
and short notices of their contents, in order to show, in chronological order, the 
views held respecting them at different times; and, further, to render the subject 
more readily intelligible to those who have not made a special study of this group 
of organisms, I have entered in some detail into the characters of the group gene- 
rally, referring more particularly to the skeletal structures and to their condition 
of preservation, this last being a subject of special importance in connection with 
fossil Sponges, since the changes they have undergone have, in very many instances, 
completely masked their original features, and given rise to much of the miscon- 
ception respecting their true characters. 
