No. 501] THE FLORISSANT EXPEDITION OF 1908 571 



two other species, T. foliarum Cope, and T. copei Osborn, 

 Scott and Speir, were added from the Florissant shales. 

 T. copei, which has not been figured, is stated to differ 

 from T. foliarum by its smaller scales. The genus is one 

 of quite unusual interest, because it appears to belong 

 to the suborder Xenarchi, an old group with peculiar 

 anatomical characters, represented to-day by a single 

 species, Aphredoderus sayanus, confined to the eastern 

 United States. According to Jordan and Evermann, the 

 Xenarchi are related to the Percopsidae, of which two liv- 



ing species are known— Percopis guttatus Agassiz, from 

 the Great Lakes and surrounding regions, and Columbia 

 transmontana Eigenmann, from the Columbia Eiver. 

 These fishes are evidently remnants of an ancient fauna, 

 which in Tertiary times included a variety of genera and 

 species. Agassiz, when describing Percopsis, was much 

 impressed by its generalized features, combining char- 

 acters which commonly existed together in Cretaceous 

 fishes, but are widely separated in modern forms. " Now 

 my new genus Percopsis is just intermediate between the 

 Ctenoids and Cycloids ; it is what an ichthyologist at pres- 

 ent would scarcely think possible, a true intermediate 

 type between Percoids and Salmonida?" (Agassiz, 1850). 

 It is remarkable that this relic of earlier days should now 



