80 THE ZOOLOGIST. 



or 227 species of Unio to be found in the rivers and pools 

 of France. Doubtless we have to recognize the fact that these 

 two forms are extremely variable, but once we begin to describe 

 individual differences, we commence a task which may have no 

 ending. 



M. Locard's method, it is true, makes us acquainted with a 

 larger number of described forms than are to be found in the 

 works of his predecessors, but this does not mean any great 

 advance in the science. 



Moreover, although M. Locard describes the shells very 

 minutely, he ignores the animals inhabiting them. Had he 

 selected a typical species for example in each genus, and given us 

 a description of the mollusc, with some account of its mode 

 of life and reproduction, he would have added considerably to 

 the value of his treatise. 



As it is, he has produced a book rather for the shell-collector 

 than for the naturalist, and might have made it even more useful 

 to the former, had he described the sort of situation in which each 

 species is to be found. It is not enough to say of Physa acuta, 

 for example, " commun ; presque partout, surtout le centre et le 

 Midi." The collector wants to know whereabouts to look for it ; 

 whether in stagnant water, or running streams; whether buried in 

 the mud from which it must be dredged ; crawling amongst the 

 herbage on the bank ; or adhering, perhaps, to the under side of 

 the leaves of some Nymphcea, Nuphar, or other water-plant. 



As to the figures in the text, of which there are about 300, 

 they have been carefully drawn, no doubt ; but many of them, as 

 Limnaa and Physa are, as one may say, "un peu trop solide." We 

 miss the delicacy, lightness, and semi-transparency which charac- 

 terise these shells, and serve to distinguish them at a glance 

 amongst their fellows. 



On the whole, then, we are disappointed with M. Locard's 

 book, though we cannot but admire his great power of discern- 

 ment, and the extraordinary industry which he has displayed in 

 collecting and describing so large a number of shells. 



