CHAPTER VI. 



This report is based upon the entire collection of fishes made in Nevada, 

 Colorado, Utah, New Mexico, Arizona, and California, during the years 1871, 

 1872, 1873, and 1874, by the different nauralists attached to the expedition. 



Of the collection of 1871, made by Mr. F. Bischoff, but few specimens 

 remain to attest the painstaking industry of this well known collector, most 

 of them having been destroyed by fire before reaching this office. For- 

 tunately, with the exception of one can of specimens destroyed by leakage 

 of alcohol, the collection of 1872 reached Washington in good condition, as 

 did that of 1873 ; and it will be found that, from this material, most valua- 

 ble information has been acquired relative to the western forms of ichthyic 

 life. 



As one of the most valuable results derived from a study of the collec- 

 tion, it appears that the basin of the Colorado River is the habitat of a small 

 group of fishes of the family Cyprinidce, which may be called the Plagopterince, 

 which embraces three genera Plagopterus, Cope ; Lcpidomcda, Cope ; and 

 Meda, Girard. The group differs from others of the family in the posses- 

 sion of two strong osseous rays of the dorsal fin, the posterior of which is 

 let into a groove in the hinder face of the anterior without being coossified 

 with it, thus constituting a compound defensive spine. The rays of the 

 ventral fin, excepting the first and second, are similarly modified. The 

 greater part of their length consists of an osseous dagger-shaped spine, with 

 grooved posterior edge, Avhich overlaps the border of the succeeding ray, 

 when the fin, like a fan, is closed up. The articulated portion of the ray 

 either emerges from the groove below the free acute apex of the spine, or 

 appears as a continuation of the apex itself. It is worth observing that the 

 only other instance of this ossification of the ventral rays is to be seen in 



G37 



