INTRODUCTION. 



There is a considerable literature dealing with the fresh-water fishes of Mexico and 

 Central America, but our knowledge of them must still be regarded as very incomplete. 

 The fact that not a single fresh-water fish has yet been described from the Republic of 

 Honduras, or from Nicaragua north and east of the Great Lakes, may be instanced in 

 support of this. The following account is based on the material in the British 

 Museum ; the diagnoses of the sub-orders and families in the systematic part are 

 intended only to apply to their Mexican and Central- American representatives ; in all 

 cases synopses of the genera and species are presented in the form of keys, and 

 sufficient references are given for the verification of determinations thus effected. 

 Detailed descriptions and full synonymies are given only in the case of groups 

 which appear to need revision and which are well represented in the British 

 Museum. 



True fresh-water fishes and also marine fishes which are known to ascend rivers 

 beyond the influence of the tides are included : thus, in addition to the problems of 

 the distribution of nearctic and neotropical types in this area, that of the differentiation 

 of the marine faunas of the Atlantic and Pacific coasts is dealt with to a certain 

 extent. The introductory remarks are arranged under the following headings : — 



1. Principal Faunal Works on the Fresh-water Fishes of Mexico and Central 



America. 



2. Principal Collections described in this Work. 



3. Classification. 



4. Geographical Distribution. 



5. The Shore-Fishes of the Atlantic and Pacific Coasts of Mexico and Central 



America. 



