PROCEEDINGS OF THE NATIONAL MUSEUM. 



125 



Morone) is probably a member of a different family. The European 

 Percids seem naturally to fall into the following groups: 



PtTcariiia. 



Perca. 



Stizostedion. 



Acerina. 



Gymnocephalus. 



Cingla. 



Aspro. 



The relationship of Perca and Stizostedion is especially close. 

 The order of the differentiation of the genera from a primitive type 

 may be expressed by the following genealogical tree. 



Percarina. 



Perca. 



Stizostedion. 



^. QTO 



Asjrro appears to be the nearest European relation to the American 

 Etheostomiues ; at least it resembles them most in appearance and the 

 form of the ventrals. 



It will be noti('ed that the character first appreciated by Mr. Boulen- 

 ger (the relative width of the interspace between the ventral fins as com- 

 pared with the width of the bases of these fins) is coordinate with the 

 characters previously recognized by Dr. Jordan and myself and there- 

 fore corroborates the approximation of the European species and their 

 segregation from the American forms. The evidence therefore appears 

 to be strong in favor of the difi'erentiation of the genus into two pri- 

 mary sections, one including the European fishes and the other the 

 American. The Liicioperea marina or Stizostedion marinum conse- 



* Gymnocephalus (Bloch) BIkr. Arch. N^erland Sc, vi. 11, p. 2m,=Lepto2)erca (Gill 

 Proc.Acad. Nat. Sc. Phila., 1861, p. 502) is distinguished from Acerina by the slender 

 body, prolonged snout, and longer, niany-spined (17—19) dorsalis. Its species are 

 G. schrcetzer (ex Linn) and G. tanaicensis (ex Guldenstedt). 



