vi Prejace. 



The types which are described here, as well as the general 

 facts of animal structure, have been dealt with by so many 

 zoologists in so many text-books, that it is hard to illustrate 

 them by fresh drawings. It is quite useless, for example, to 

 attempt to improve upon the excellent figures of the crayfish 

 appendages to be found in Mr. Huxley's " The Crayfish." 

 Such illustrations I have copiously borrowed from various 

 sources, which are duly acknowledged in the case of each cut. 



Among these will be noticed a few new illustrations, either 

 copied from the original memoirs which they illustrate or modi- 

 fied from existing wood-cuts in text-books; these are Figs. 1-7, 

 9-13, 22-25, 27-32. 34, 37-41. 43, 45-49, 52, 63, 73, 74. 76. 

 For these I am indebted to the skill of Mr. R. E. Holding. 



F. E. BEDDARD. 



