VI. 
PREFACE. 
aud advice upon many critical points, and has at all times placed his 
great knowledge and experience freely at my disposal, a favour I cannot 
too cordially acknowledge. 
Many other friends have likewise contributed valuable and valued 
information and assistance, and most of these obligations liave been 
acknowledged in their appropriate places in the text, but the willing 
co-operation of many other well-wishers has been invaluable, and I 
may especially mention Mr. R. D. Darbishire and Mr. Robert Welch, 
to whom I am under so many and such varied obligations for their 
unwavering interest in, and practical sympathy with, my labours, that 
thanks are inadequate to express my appreciation of their help. 
Although more than six years have been occupied in the production 
of the present volume, the time cannot be considered excessive when 
it is remembered that my time cannot be devoted exclusively to the 
work and that the whole of the labour has devolved solely upon 
myself, not only as regards the preparation of the text, but also in 
producing the drawings and photograms from which the whole of the 
737 figures or maps have been engraved or lithographed. 
Financially, the work is not and cannot be a success, as no expense 
has been spared to attain the very best results, so that even if the 
whole of the small edition that has been prepared becomes exhausted, 
the proceeds will not be nearly sufficient to repay even the pecuniary 
outlay involved in its production. 
The portion of the work devoted to genera and species will be com- 
menced without unnecessary delay and, it is hoped, will be quickly 
completed, but to attain this desirable result I must bespeak the 
active aid of all those interested in the subject. 
JOHN W. TAYLOR. 
North Grange, Horsforth, 
Leeds, Dec. 29th, 1900. 
