Reviews —Dr. H. Rauff—On Fossil Sponges. 525 
geological horizons of the sponges described in them; which will 
materially facilitate the hunting out of references. Next comes 
a long chapter on the literature of the group, in which the various 
views and systems of different authors are explained and discussed. 
It is somewhat depressing to see from this what a large amount 
of earnest labour has been wasted, on what we now recognize to 
be thorough failures to understand the real nature of these organisms, 
and this groping in the dark lasted to pretty well up to 1876. 
Succeeding chapters treat of the Morphology, the Histology (as 
known from living forms) and the Canal system in fossil sponges, 
and the author describes nine different modifications of the canal 
system as shown by the skeleton. The mode of increase is then 
referred to, and the puzzling question as to what constitutes an 
individual or a colony. Next comes the important subject of the 
nature and form of the various kinds of spicules in siliceous and calci- 
sponges, and the mode of their union in the case of the former of these. 
In the classification the author considers the Sponges, as a whole, 
to belong to the Metazoa rather than to a separate sub-kingdom. 
Four orders of siliceous sponges are recognized, ‘ Hexactinellida, 
Tetractinellida, Monactinellida, and Ceratosa.’ This last may be 
“neglected, since no fossil forms belonging to it are as yet known, 
and of the other three it may be said that paleontologists are mainly 
concerned with only two groups, the Hexactinellids and the Lithis- 
tids, since with rare exceptions, all the forms of fossil siliceous 
sponges are included in them, though we know from the abundance 
of the detached spicules of Monactinellids and Geodine Tetractinellids 
that sponges of these divisions were probably as numerous in the 
past as at the present day. In one or two points the classification 
put forward is open to criticism, thus for example, the Placo- 
spongide, with their dermal crust of globate spicules, quite undis- 
tinguishable from those of the Geodine Tetractinellids, are yet 
reckoned as Monactinellida; and there is much to support the view 
that most of the other families placed in the tribe Clavulina have a 
good claim to be considered as modified Tetractinellids. 
As regards the Calcisponges, the author ranks all the known 
forms, fossil and recent—with one exception—under a new order, 
the Dialytina. The solitary exception is a very remarkable new 
form from the coast of Japan, at present very briefly described and 
not yet figured, which Dr. Doderlein states has the spicules connected 
together in the same way as in the siliceous Lithistids. This new 
form stands as the only representative of the order Lithonina. 
There is one particular feature in this work to which exception 
may be taken, and that is the excessive use of terms taken from the 
Greek to designate the various forms and parts of spicules. In this 
matter Dr. Rauff may plead that he has followed the example of 
some of the principal writers on recent sponges during the last few 
years, who have agreed to cast aside, with very few exceptions, all 
the terms previously employed in spongiology and replace them by 
new Greek ones. To make matters worse, these authorities are not 
always agreed as to the most suitable Greek words to employ, though 
