ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
513 
Bryozoa. 
Catalogue of Fossil Bryozoa in the British Museum/ — Dr. J. W. 
Gregory has selected the Jurassic Bryozoa for the first volume of the 
Catalogue of the Fossil Bryozoa in the Department of Geology of the 
British Museum. The selection of these for the first catalogue may 
seem capricious, hut it was, the author tells us, made deliberately. The 
two orders of Bryozoa that prevailed in the Palaeozoic era became extinct 
or greatly reduced in importance at its close. Jfc is among the Jurassic 
deposits that we have to seek for the ancestors of the existing types of 
this group. They occur there, Dr. Gregory adds, with the primary 
lines of divergence well marked, and not obscured by the extreme 
secondary variations of later periods. In an exceedingly interesting 
introduction, the author commences with a discussion of the problem of 
tubular fossils. He points out that one of the most similar ways in 
wdiich aquatic animals seek protection from their enemies is by surround- 
ing themselves with a tube. As these tubular shells arc the most easily 
acquired of all effective methods of defence, they have been adopted 
independently by animals occupying very different zoological positions, 
and they may be cither simple tubes or elaborate skeletons. Examples 
are given from various groups of the Animal Kingdom, and it is pointed 
out how, in these different groups, the same forms of tube may again 
and again be met with. Most of the tube-dwelling forms live in shallow 
waters, where they are exposed to powerful currents and tides, and need 
shelter from the sand and shingle. The study of fossil worm-tubes has 
been abandoned in despair, for, so far as we can see at present, they can 
give no aid in the classification of the group to which they belong. In 
the case of the Bryozoa, however, these fossils cannot be ignored like 
the Worms ; their evidence, therefore, must be considered in any attempt 
to trace the evolution of the Bryozoa. The author readily admits that 
there are no diagnostic characters by which we can positively say 
whether a given fossil is a Bryozoon or not. He includes in the present 
catalogue certain fossils which have often been assigned to corals, while 
he rejects others which have been previously considered as belonging to 
the group. 
With regard to the affinities of the Bryozoa, we must know more 
than we do at j>resent before we can definitely determine their exact 
relationships. The author deals in some detail with the characters of 
the shells, and goes on to discuss the value of generic divisions in the 
Cyclostoma. A consideration of various points raises the question 
whether there arc such things as genera and species among the cyclo- 
stomatous Bryozoa. Dr. Gregory points out that in the case of the 
Echinoidea the term “ genus ” has a fairly definite value. For example, 
the two commonest living English Ecliinoids are Echinus esculentus 
and E. miliaris. The distinctions between these species were nearly 
as well marked in the period of the Crag as they are at present. Kow 
if x represents the number of generations which lived in that division 
of geological time known as an age, then these two species have been 
distinct for at least 5 x generations, and their common ancestor lived 
7 x generations ago. Similarly with genera. This is enough to show 
* ‘ The Jurassic Bryozoa,’ 8vr>, London, 1896, 239 rp., 11 pis., and 22 figs. 
