geological events and their implications to the evolutionary history of the taxonomic 

 groups; the most informative studies have been of various characiform fishes (e.g., 

 Vari 1988, 1989a, 1989b, 1989c). Relationships in most groups of neotropical 

 catfishes are unresolved, and no major phylogenetic studies have included 

 discussions of historical biogeography. Since hypotheses about the role of vicariance 

 in speciation require well-resolved phylogenies, there are presently few catfish 

 groups that are available for zoogeographical analysis. 



Based on extensive studies of curimatid characiforms, Vari (1988) recognized 

 ten major regions of endemism in South America. The most thoroughly studied 

 region is at the northern reaches of the Andes, where the fauna has been most 

 intensively studied cladistically, and where there are several subregions of 

 endemism. The remaining regions correspond largely to physiographically distinct 

 areas of the continent, associated with major river systems. The largest area 

 encompasses the Amazon itself. Other regions include the following: Orinoco • 



basin; coastal rivers to the northeast of the Guiana Shield; the Rio Sao Francisco 

 basin; separate coastal areas to the north and south of the Rio Sao Francisco; and, 

 the Parand-Paraguay system, which is separable into upstream and downstream 

 divisions. Ageneiosids occupy all of these regions except the Rio Sao Francisco 

 drainage and the coastal drainages to the south. 



The widespread distribution of most species of ageneiosids, and their 

 relatively poorly resolved relationships, precludes a thorough evaluation of their 

 zoogeography. There are, however, several noteworthy considerations. 



Ageneiosus pardalis is the only ageneiosid occurring west of the easternmost 

 Andean cordillera. It is found in the Lake Maracaibo basin, and occurs westward in 

 the major drainages of northwestern Colombia and southern Panama. This 

 distribution parallels that of a number of other species (Vari 1988). Schultz (1944) 

 considered the Maracaibo population to be specifically distinct from the more 



'■ ' ' -i ; 



