4 PREFACE. 



In the preparation of the second edition, it was " found necessary 

 to entirely recast the account of the Fishes, in order to include 

 the results of recent investigations in that department. The 

 author has availed himself of this opportunity to substitute for 

 the artificial keys in the previous edition, a series of generic 

 diagnoses, which, while serving the purpose of a ' key,' also serve 

 to express the true relations of the species." The author regrets 

 that this change can not in the present edition be extended to all 

 the groups included in the work, as well as to the Fishes. 



D. S. J. 



Bloomington, Ind., Not., 1879. 



