SHELLS AND THEIR INHABITANTS. 129 
they can with difficulty, if at all, be recognised from their sur- 
roundings. We are enabled, by the courtesy of the publishers, 
to give figures of these. The analogy of the caddis-worm and 
its case will of course occur to all. 
The section on variation is very interesting, and the full page 
illustration of the different forms of the common dog-whelk 
{Purpura lapillits) ought to teach a useful lesson to certain be- 
nighted shell collectors, who spend their lives inventing a new 
name for every shell that shows some slight difference in form 
from its brothers. “ Shells as ornaments ” we must not dwell 
on, nor on “ Mollusca as food for man,” although “ Oysters 
under the Romans” sounds a tempting theme. “Snails as 
medicine” and “ Prices paid for shells ” conclude this, the most 
attractive part of the book to the general reader. The student 
will find the chapters that follow, on the anatomy of the mollusca, 
very helpful to him, though both in this and the systematic 
portion of the work, with which the labours of Mr. Cooke are 
brought to an end, he will do well to bear in mind the golden 
rule that there is no royal road to any branch of learning, and no 
single book can ever be entirely relied upon. 
Of the chapters that come between these two last-named 
subjects, and deal with the distribution of the mollusca, nothing 
need here be said, for they are of necessity tough reading even to 
the expert ; and though Mr. Cooke has done as well as man 
could to make them readable, the abundance of scientific names 
on every page renders them dry pabulum indeed, despite the 
excellent figures that occur at intervals, veritable oases in a 
desert. 
Indeed, with but few exceptions, the figures throughout the 
Zenophora i^Phorus) conchylio^hora. 
Born., concealed by the stones which 
it glues to the upper surface of its shell. 
(From a British Museum specimen.) 
Zenophora {Phorus) pallidula^ Reeve. A 
mollusc which escapes detection by covering 
itself with dead shells of other species. (From 
a Challenger specimen in the British Mu- 
-seum, X A.) 
