NORTH AMERICAN REGION. 247 



studied than those of Europe ; of many scarcely more than 

 the name is known. This also applies in a great measure to 

 the Salmonoids, of which only half as many as are found in 

 the Paltearctic region have been sufficiently described to be 

 worthy of consideration. North America will, without doubt, 

 in the end show as many distinct races as Europe and Asia. 



Cyprinoids, belonging to genera living as well as extinct, 

 existed in North America in the tertiary period. At present, 

 Cyprinina, LeucisciTict, and Ahramidina are well represented, 

 but there is no representative of the Old World genus Barlus, 

 or of the Cdbitidina ^ ; Rhodeina are also absent. On the 

 other hand, a well-marked Cyprinoid type is developed — 

 the Catostomina, of which one species has, as it were, re- 

 turned into Asia. Very characteristic is the group of Centrar- 

 china, allied to the Perch, of which there are some thirty 

 species ; two Grystina. Of the Sticldebacks there are as 

 many species as in Europe, and of Pike not less than seven 

 species have been distinguished. Umbra appears to be 

 as local as in Europe. Some very remarkable forms, types 

 of distinct families, though represented by one or two species 

 only, complete the number of North American autochthont 

 fishes — viz., Aphredodems, Fercopsis, Hyodon, and the Hetcr- 

 opygii (Amhlyopsis and Cholog aster). The last are allied to 

 the Cyprinodonts, differing from them in some points of the 

 structure of their intestines. The two genera are extremely 

 similar, but Chologaster, which is found in ditches of the rice- 

 fields of South Carolina, is provided with eyes, and lacks the 

 ventral fins. Amhlyopsis is the celebrated Blind Fish of the 

 Mammoth Cave of Kentucky : colourless, eyeless, with rudi- 

 mentary ventral fins, which may be occasionally entirely 

 absent. 



1 Cope has discovered in a tertiary freshwater-deposit at Idaho an extinct 

 gemis of this group, Diasiichus. He considers this interesting fact to be 

 strongly suggestive of continuity of territory of Asia and North America. — 

 "Proc. Am. Phil. Soc. 1873," p. 55. 



