PREFACE 



mere process blocks, they will show more detail when examined 

 with a lens. 



While sparing no pains to ensure the authenticity of the speci- 

 mens sent me, and carefully checking them with others from other 

 sources, there still remains a margin for error, therefore the 

 authority for the name has always been quoted. I shall be under 

 a personal obligation to any of my readers who will point out 

 any mistakes. Wherever I have felt any doubt, the name is 

 followed by a note of interrogation, and in such cases I have 

 refrained from quoting the alternative names, except such as have 

 been supplied to me with the specimens. 



Finally, I wish to acknowledge the hearty support of my col- 

 league Mr. Arthur Deane, to whose skill in preparing the photo- 

 micrographs so much of the value of this book is due, and to 

 my friend Mr. Philip E. Martineau for his kindness in looking 

 over the proofs. 



HERBERT STONE. 



Bracebridge Street, Birmingham. 



IX 



