FISHES OF LAKE SUPERIOR. 285 



class. Now the genus Percopsis is as important to the understanding 

 of the modern types of fishes as Lepidosteus and Cestracion are to 

 the understanding of the ancient ones, as it combines characters which 

 in our day are never found together in the same family of fishes, but 

 which in more recent geological ages constituted a striking peculiar- 

 ity of the whole class. My Percopsis is really such an old-fashioned 

 fish, as it shows peculiarities which occur simultaneously in the fossil 

 fishes of the chalk epoch, which however soon diverge into distinct 

 families in the tertiary period, never to be combined again. 



This ancient character of some of the American fishes agrees 

 most remarkably with the peculiarity of the vegetation of this conti- 

 nent, which, as I have shown on former occasions, resembles also 

 the fossil plants of prior ages. 



The geographical range of these peculiar, old-fashioned beings is 

 also very remarkable, they living in temperate, or rather cold climates, 

 when their earlier representatives lived in warmer epochs. 



The most striking features of the fishes of the tertiary period and 

 those of our time consist in their belonging to two groups of the class 

 only ; one, the Ctenoids, with rough, combed scales, in which the re- 

 spective representatives have also prominent serratures on prominent 

 spines upon the head, in the operculum in particular, and in the fins ; 

 the other, the Cycloids, smooth, with simple scales with an entire 

 margin, in which some few types however have also spinous fins. 



Now my new genus, Percopsis, is just intermediate between 

 Ctenoids and Cycloids ; it is, what an ichthyologist, at present, 

 would scarcely think possible, a true intermediate type between 

 Percoids and Salmonidge. 



The general form of this genus reminds us of the common perches, 

 but it is easily distinguished from them, by the fact that its head and 

 the opercular apparatus are smooth and unprovided with denticula- 

 tions, as also by the presence of a small adipose fin, as in the salmons. 

 The anterior dorsal is also a small fin, composed of soft branched ar- 

 ticulated rays, as in the salmons. The ventral fins are placed at 

 the middle of the abdominal cavity, as in the Abdominales in general. 

 The scales, however, are truly serrated as in the Percoids, a struc- 

 ture which, as far I know, does not occur in any of the Abdominales. 

 The conformation of the mouth is also as in . the perches, that is to 



