Preface. vii 



the subject in question, and I have drawn from these material suited 

 to my purpose. In the sequence of the orders and families I have fol- 

 lowed Jordan and Evermann in Bull. 47, U. S. Nat. Mus. The 

 sequence of genera and species has been changed whenever, in the 

 light of new information, it appeared necessary. I have also 

 made free use of the publication above mentioned for material 

 in the characterization of orders and families. A special effort has 

 been made to bring together, in as useful a form as possible, our pres- 

 ent knowledge of the fresh-water fishes of Mexico north of the Isthmus 

 of Tehuantepec. The study of this group of animals in this region 

 is of especial interest, for between these two lines is the meeting place 

 of the northern and the tropical faunas. In this respect these boun- 

 dary lines are in a measure natural ones, because very few species of 

 tropical fishes reach the northern line, and but few northern repre- 

 sentatives are found farther south than the Isthmus of Tehuantepec. 

 In addition the subject presents very interesting material for a study 

 in geographical distribution. 



