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Changing Fish Fauna of the Southwest 381 spinedace.-This subspecies was endemic to a single spring-fed marsh near Panaca, Lincoln County, Nevada, in the basin of Meadow Valley Wash, a flood tributary to the Virgin River (Hubbs and Miller, 1948, pp. 98-100, map 1, no. 65). Recent agricultural modifications of the area and the introduction of exotics, especially Gambusia a. af- finis, are held to be important factors that led to the extermination of this localized population, sometime between 1938 and 1959 (Miller and Hubbs, 1960, pp. 21-23). Pantosteus species: This sucker has been collected only once, in 1938, at the northern end of Spring Valley, eastern Nevada (Fig. 1). In an effort to obtain further specimens, Carl L. Hubbs and I re- visited Spring Valley in 1959 and thoroughly worked the same stream where the species was collected 21 years earlier. No specimens were secured. Other waters in the valley bottom were either fishiess or contained only a small minnow; mountain streams have only planted trout. Deterioration of stream flow is a plausible explanation for the extinction of this endemic sucker. Cyprinodon radiosus Miller, Owens Valley pupfish -This species, restricted to the northern part of Owens Valley, California, was formerly abundant in ditches, sloughs, swamps, and bog pastures that 9 featured this part of the valley in the early 1900'x. The population j was then sufficiently large to serve as an effective means of mosquito i control. As its habitat suffered through tapping of the water supply and drainage of the swamps, the species began to decline; introduc- tion of exotics, particularly largemouth bass, presumably hastened its disappearance (Miller, 1948, pp. 94-95). The species has not been taken since 1939 and in all probability is now extinct. Cyprinodon bovinus Baird and Girard, Leon Springs pupfish.- This species is known only from Leon Springs (Clark Hubbs, 1957, p. 101), about 8 miles west of Fort Stockton (Fig. 1), Pecos County, Texas. It was described from 16 specimens taken in 1851 and, to my knowledge, has not been collected since then. In 1938, Carl L. Hubbs attempted to secure material and in 1950 Howard E. Winn and 'I worked the spring sources and their outlets exhaustively but to no avail. Local testimony in 1950 asserted that the spring heads had been treated with rotenone ("about 4 or 5 years ago") for the purpose of eliminating the hordes of carp. The Leon Springs pupfish probably disappeared through the combined attack of habitat restriction, modi- fication of the source springs it lived in, and the introduction of such r,