no BIBLIOGRAPHY. 



The third section of the work is devoted to detailed 

 treatment of particular distribution, and is full of very valuable 

 notices, and indications for further research and generalization. 

 It shows, besides a comprehensive selection of such notices for 

 the old continent, a compendium of the observations of North 

 American observers as to the forms which are common over 

 the whole arctic province, or which are representative in the 

 two hemispheres, or which appear to have passed with emigrants 

 to the new world. 



The Germanic regions and those called the North Russian 

 and Siberian, and the Celtic (N.W. France, Britain, and 

 Ireland), receive full attention. There follows an interesting 

 disquisition on the mollusca which occur in the higher moun- 

 tain districts, the Pyrenees, the Alps, the Carpathians, and the 

 Caucasus, full notes on the region of the Mediterranean and 

 a too short section on the mollusca of the province of tropical 

 Asia. 



The book concludes with a useful list of books and papers 

 referred to, eight plates illustrating variations in the forms of 

 Unios, and a table of species and occurrence. This table is in 

 itself a very remarkable contribution to the subject. Enumera- 

 ting 739 species (with the addition of 13 more to the end of 

 1882) it gives, in 14 large sheets, notes of the occurrence in no 

 less than 88 (larger or smaller) districts. In this list the 

 author has noted his facts up to, apparently, the last mentioned 

 date. Such a table, as indeed the essay itself, is of a kind that 

 must necessarily soon require supplementing, and no doubt 

 correction ; but the value of such a work is great and well 

 worth the labour spent upon it, or in mastering its details, and 

 one can well sympathize with Herr Jordan's modest satisfaction 

 in seeing it in print. 



The book will for many years be at once a store-house and 

 a platform in this department ; to which every student must have 

 recourse, and on which many observers will arrange their new 

 facts, and will not soon be superseded by a better. — R.D.D. 



J.C, iv., July, 1884. 



