94 BRITISH PALAOZOIC SPONGES. 
characters of genera and species, based on skeletal fragments or even on detached 
spicules merely, must be limited and provisional, but at the same time there is no 
reason to doubt that these fragments and spicules really represent distinct species, 
and may justly be regarded as such. 
Owing to the indefinite ideas formerly held as to the nature of fossil Sponges, 
it has been my especial endeavour to examine the type specimens of all the species 
hitherto described. The desirability of this revision of authentic specimens is 
shown by the long list of bad and doubtful species given in the sequel. Of the 
total number of reputed species of Palaeozoic Sponges up to 1883, I find that only 
one-third belongs to the group, the remaining two-thirds being either too obscure 
for determination or pertaining to other organisms. 
In the preparation of this part of the Monograph I have received much 
valuable assistance from numerous friends and fellow-workers, to whom I return 
my warm acknowledgments. The fossil Sponges preserved in the National 
Museum at South Kensington, in the collections of the Geological Survey 
at Jermyn Street, and at KHdinburgh, and in the Woodwardian Museum at 
Cambridge, and the University Museum at Oxford, have freely been placed at my 
disposal; and to Dr. H. Woodward, F.R.S., Dr. A. Geikie, F.R.S., Prof T. 
McKenny Hughes, M.A., and Prof. J. Prestwich, F.R.S., my thanks are especially 
due for the opportunities of studying them. I am also under great obligations 
to Mr. John Smith, Kilwinning, Mr. John Young, F.G.S., Hunterian Museum, 
Glasgow, Dr. J. R. 8S. Hunter, Carluke, and Mr. James Bennie, Edinburgh, for the 
unstinted loan of their private collections from the Carboniferous series of Scotland ; 
whilst Mr. J. Wright, F.G.S., Belfast, sent me his specimens from the same series 
in Ireland. Prof. R. J. Anderson, M.A., enabled me to examine the type collection 
of supposed Permian Sponges described by the late Prof. King, and now in the 
Museum of Queen’s College, Galway. I have also received many specimens, 
including type forms, from my friend Mr. H. J. Carter, F.R.S., Prof. H. Alleyne 
Nicholson, F.L.8., Prof. C. Lapworth, F.G.S.,.Mr. G. H. Morton, F.G.S., Mr. J. 
Thomson, F.G.S., Glasgow, and the late Mr. A. Champernowne, F.G.S. 
GENERAL Features or tae British Patmozoic SPonGEs. 
Notwithstanding their unfavorable state of preservation, the presence in the 
British area during Paleozoic times of representatives of the various existing 
sub-orders of siliceous Sponges can be undoubtedly proved; and, in addition to 
members of the Monactinellidew, Tetractinellide, Lithistide, and Hexactinellide, 
there are other forms, included in the Octactinellide and Heteractinellide, which 
are not as yet known later than the Carboniferous period. 
