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," " CHAPTER VI. This report is based upon the entire collection of fishes made in Nevada, Colorado, Utah, New Mexico, Arizona, and Califomia, 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 mnterial, most valua- ble information has been acquired relative to the westem 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~Pla[Jopterus, Cope; Lepidomeda, 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, excel)ting tbefirst and second, are similarly modified. The greater part of their length consists of an osseous dagger-shaped spine, with grooved posterior edge, which overlaps the border of the succeeding ray, when the fin, like a fan, is dosed up. The articulated portion of the ray either emerges from the groove below the free acute apex of the spine, 01' appears as a t~OI;tinuatioll of the apex itself. It is worth observing that the only other instance of this ossification of the ventral rays is to be seen III (j~7