^°i89i!^'] PROCEEDINGS OF THE NATIONAL MUSEUM. 23 



vent tbe ready iiiterniingliiig' of the two faunas. Wallace says on this 

 subject: 



Tlic wliole cliavacter of neotropical zoology, ■whether as regards its deficiencies or 

 its specialties, points to a long- continnance of isolation from the rest of the world, 

 with a few very distant periods of iinion with the northern continent. The latest 

 important separation took place hy the snbmergence of parts of Nicaragua and Hon- 

 dnras, and this separation probably coutiunad thronghont innch of the Miocene and 

 Pliocene periods; but some time previous to the coming on of the glacial epoch, the 

 union between the two continents took place which has continued to our day. Earlier 

 submergences of the Isthmus of Panama probably occurred, isolating Costa Rica and 

 Veragua, which then may have had a greater extension, and have thus been able to 

 develop their rich and peculiar fauna. 



The Isthmus of Tehuantepec, at the south of Mexico, may probably also have been 

 submerged; thus isolating Guatemala and Yucatan, and leading to the specialization 

 of some of the peculiar forms that now characterize those countries and Mexico. 



EXPLANATIONS. 



The species are numbered consecutively from first to last; tbe sub- 

 species have added the letters a, b, c, etc., to the number of their re- 

 spective species. 



Species iusufiflcieutly described or doubtful for other reasons have 

 their number followed by an interrogation point. 



As far as possible with the present status of South American ichthy- 

 ology the species of a genus have been grouped under their respective 

 subgeneric names. 



The families have been arranged, with slight modifications, after the 

 system proposed by Cope and Gill. Those families and genera which 

 have been reviewed by us have their genera and species arranged as in 

 our Eevisions. The genera and species of the other families have been 

 arranged as in Giinther's Catalogue of Fishes. 



As in the A. O. U. Code and Check-list the name of each species and 

 subspecies is followed by the name of the original describer inclosed 

 in parentheses if it is not also the authority for the name adopted. 



In selecting names we have tried to follow the canons of the A. O. U. 

 Code implicitly in all cases but the following : 



Canon xvn is to be modified to read: Between competitive, specific, 

 or generic names published simultaneously in the same work preference 

 is to be given to that which stands first in the book. 



Canon xviii is to be disregarded. 



Canon xxv is made to read : A genus formed by the combination 

 of two or more genera takes the name first given in a generic or sub- 

 generic sense to either or any of its components. 



After the name of the describer, is given the general habitat of the 

 species. All the localities at which a species has been found have been 

 compiled and on these notes the statement of the habitat of each species 

 is based. 



The habitat is followed in each case by a reference to some descrip- 

 tion of the species in question. If it is described in Dr. Giinther's Cat- 



