In the Arkansas River system in Kansas there are marked differences between fish faunas of the western and eastern parts of the state. This can be illustrated by comparison of Spring River in Cherokee County with the Cimarron River in southwestern Kansas. Single collections from Spring River or its tributaries usually contain 25 or more species of fish. Collections from the Cimarron rarely contain more than five or six species. Many of those fishes found in Spring River are characteristic of an Ozarkian fauna, and some are endemic to the Ozark uplands. Fish found in the Cimarron or Arkansas in western Kansas are members of a plains fauna of wide distribution. There is mingling of these two faunal groups across the state, with the number of Ozarkian species diminishing westward, and certain plains species diminishing eastward. A number of species such as _Moxostoma duquesnii_ and _Notropis spilopterus_ are limited, on the basis of present records, to Spring River and its tributaries in Kansas. Others have not been taken west of the Neosho drainage. The Verdigris River provides the next major avenue of westward dispersal followed by Caney River, Grouse Creek, and the Walnut River. West of the Walnut River system Ozarkian species have been almost always absent from collections. The Chikaskia River is somewhat exceptional. Moore and Buck (1953) reported from this river several species that seem more typical of eastern faunal associations. Table 10 indicates the stream system in which the present westernmost records are located for a number of fishes found in the Arkansas River system in Kansas. TABLE 10.--PRESENT WESTERNMOST RECORDS OF SOME FISHES IN THE ARKANSAS RIVER BASIN IN KANSAS. Spring River _Cottus carolinae_ _Dionda nubila_ _Etheostoma blennioides_ _Etheostoma gracile_ _Etheostoma nigrum nigrum_ _Etheostoma punctulatum_ _Etheostoma saxatile_ _Hypentelium nigricans_ _Moxostoma duquesnii_ _Notropis spilopterus_ _Noturus exilis_ Neosho River _Cycleptus elongatus_ _Etheostoma chlorosomum_ _Etheostoma flabellare lineolatum_ _Hybopsis amblops_ _Hybopsis biguttata_ _Hybopsis x-punctata_ _Notropis zonatus pilsbryi_ Verdigris River _Etheostoma whipplii_ _Etheostoma zonale arcansanum_ _Percina copelandi_ _Moxostoma carinatum_ _Notropis boops_ _Notropis volucellus_ _Noturus miurus_ Chikaskia River _Ictalurus natalis_ _Percina phoxocephala_ _Labidesthes sicculus_ _Lepomis megalotis breviceps_ _Micropterus punctulatus_ _Moxostoma aureolum pisolabrum_ _Moxostoma erythrurum_ _Notropis camurus_ _Pimephales notatus_ _Pimephales tenellus_ _Noturus nocturnus_ The westernmost records for seven species are in the area studied. 1. _Lepisosteus platostomus._ 2. _Carpiodes velifer._ 3. _Moxostoma carinatum._