302 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



S Cichlasonia hedricki Meek. 



S CicJilasoma panua (Gunther). 



S CicJilasoma eigeinna^nii Meek. 



S CicJilasoma melauuriiui (Gunther). 



S CicJilasoma iiebulifer (Giinther). 



S TJioricJitJiys Jielleyi (Steindachner). 



S TJioricJitJiys ellioti Meek. 



T PJiilypnus dormitor (Lacep^de). 



T Dormitator macidatiis (Bloch). 



T CJionopJioyiis taiasicus (Lichtenstein). 



Me AcJiirus fasciatns (Lacep^de). 



Only four out of the total of thirty-seven species are northern, while 

 thirteen are distinctly tropical, of which the genera CicJilasoma and TJio- 

 ricJitJiys are largely middle American. 



The list may be contrasted with the list of the combined Geronimo and 

 Verde, directly across the headwaters of the Papaloapam and emptying 

 into the Pacific. They were fished near tide water and at an elevation of 

 nearly 5000 feet. 

 S A sty an ax cenens (-Gunther). 

 T Fundulits oxacce Meek. 

 T Gambusia fasciata Meek. 

 T Aiiableps dovii Gill. 

 T Heterandria littzi Meek. 

 T Poccilia spJicnops Cuvier & Valenciennes. 

 Me Mitgil cepJialiis Linnaeus. 

 S CicJilasoma evermanni Meek. 

 T PJiilypnus dormitor (Lacepede.). 



Of these, but two are South American, the rest are transitional. 



The tropical element has reached farther north on the Atlantic side than 

 on the Pacific, or in any cross section of the country there are more South 

 American elements in the former than in the latter. None of the South 

 American types have reached the plateau of Mexico. They skirt along 

 the coastal plain on both slopes to an elevation of perhaps 2000 feet and 

 in the Rio Grande basin to an elevation of even 3000 feet. 



