360 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



a coast line is not needed, because, first, some of the species of the Pacific 

 slope are mountain forms, some of them living on both slopes. If such 

 a genus as Pygidium has been able to establish itself from stream to 

 stream along the Andes from Guiana to Patagonia, it needs no continuous 

 waterway to explain its presence on both slopes. The same for more 

 limited reasons applies to Chcetostomus and Arges. Second, a watershed 

 of moderate height is not necessarily a barrier to the migration of fresh- 

 water fishes and several species have evidently succeeded in recent times 

 in crossing the divide in the northwest corner of the continent in one direc- 

 tion or the other, inasmuch as over 27 per cent, of the entire Pacific fauna 

 is also found on the Atlantic, a consensus which is significant and conclusive. 



Nearly all the genera found on both slopes, the exceptions to be con- 

 sidered presently, are genera of very wide distribution on the Atlantic 

 slope, reaching the Magdalena or the Isthmus of Panama. 



Only four genera are confined to the Pacific slope : Paracetopsis 

 Lebiasma, Pseudochalceiis and Saccodon. The other genera represented 

 on the Pacific slope are distributed as follows : 



1. RJiamdia. Magdalena to the Rio de La Plata and Mexico; Lake 

 Titicaca, San Francisco and Minas Geraes, p. 354. 



2. Piuielodella. Rio Chagres at Panama to La Plata ; Para to Canelos, 



P- 356. 



3. Paracetopsis. Canelos to Para ; Irisanga, p. 358. 



4. Pygidium. Andes from Venezuela to Patagonia ; French Guiana 

 and southeastern Brazil, central Argentina, p. 359. 



5. Plecostomiis. Magdalena to La Plata and Cordova ; San Francisco 

 and southeastern Brazil ; Para to Ambyiacu, p. 356. 



6. Hemiancistvus. Eastern Ecuador to Paraguay, Para and Guiana, 



P- 357- 



7. CJicctostonms. Eastern and western slopes from Peru to Panama 



and Venezuela, p. 359. 



8. Loricaria. Rio Chagres and Magdalena to Para and Buenos Aires ; 

 Calderon and Canelos, Xeberos, p. 355. 



9. Stitrisoma} Magdalena to Paraguay ; Rio Jurua, Manacapuru ; 

 Xeberos, p. 357. 



10. Arges. Andes of Peru, Ecuador, Colombia and Venezuela. 



11. Cyclopium. Andes, north of Canelos, p. 359. 



' This is probably a genus of diverse origin. 



