20 David Starr Jordan 



In a fossil herring-like fish from the Green River shales, I 

 count 40 vertebrae ; in a bass-like or serranoid fish from the 

 same locality 24, these being the usual numbers in the 

 present tropical members of these groups. 



The Pledospondyli are those soft-rayed fishes in which the 

 four anterior vertebrae are highly modified, co-ossified and 

 having a peculiar relation to the organ of hearing. The 

 Siliirida:, Cyprinidce, Catostomidcs, Characinid^, Gyninotid(z, 

 and EledrophoridcE with their relatives belong here. This 

 peculiar structure of the vertebrae is found in no other group. 

 It could hardly have arisen independently in the different 

 families, hence these great groups including the vast majority 

 of fresh-water fishes must be referred to a common stock. 



The great family of Siluridce or catfishes seems to be not 

 allied to the Isospondyli, but a separate offshoot from another 

 ganoid type allied to the sturgeons. This group is repre- 

 sented in all the fresh waters of temperate and tropical 

 America, as well as in the warmer parts of the Old World. 

 One division of the family, containing numerous species, 

 abounds on the sandy shores of the tropical seas. The 

 others are all fresh-water fishes. So far as the vertebrae in 

 the SiluridcB have been examined, no conclusions can be 

 drawn. The vertebrae in the marine species range from 35* 

 to 50 ; in the North American forms from 37 to 45, f and in 

 the South American fresh-water species, where there is al- 

 most every imaginable variation in form and structure, the 

 numbers range from 28 to 50 or more. 



The CyprinidceX also belonging to the group of Pledospon- 

 dyli, confined to the fresh waters of the northern hemisphere, 

 and their analogues, the Charadnidce of the rivers of South 

 America and Africa, have also numerous vertebrae, 36 to 50 

 in most cases. I fail to detect in either group any relation in 

 these numbers to surrounding conditions. The related Gyvi- 

 notidcz and Eledrophoridce of the tropical rivers have mau)^ 

 vertebrae. 



* Tachysurus, Felichthys, etc. 



■\ Idalurus, Anieiurtis, etc. 



X Carp, minnows, suckers, chubs, buffalo-fishes, gudgeons, etc. 



