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Figure 60. Flannelmouth sucker, 28.5 cm in total length, from the Virgin River, Ari- zona. This species remains common in the upper Colorado River basin, but has disappeared entirely from the lower basin (including the Gila River drainage) downstream from Lake Mead. moderate rapids and riffles in pursuit of bottom- dwelling invertebrates, algae, and organic debris. Bluehead mountain-suckers (Fig. 61) tend to feed on harder bottoms, scraping algal films and other organic materials (including clinging invertebrates) from rocks with their modified, cartilaginous jaws. All three of the last species breed in spring on riffles. Figure 61. Breeding adults of bluehead mountain-sucker, ca. 45.0 and 35.0 cm in total length, from the mouth of the Paria River, Arizona. This species -remains abundant within its native range in the upper Colorado River basin. Photograph by W. G. Kepner. Canyon-bound reaches of the Rio Yaqui are occupied by roundtail chubs, Yaqui suckers, and Yaqui catfish/bagre del Yaqui (Fig. 62). Beautiful shiners and Mexican stonerollers live along the banks and in quieter places. It is notable here that little sampling has been done in these reaches, which are mostly isolated and accessible only by river. It will not be surprising if future collectors in the Rio Yaqui and its major tributaries discover new species of swift-water fishes. The fish community of wider, less dramatic lower parts of the Colorado River, most of which is now dry or otherwise highly modified, consisted of a small number of special kinds, plus in its lowermost reaches a few marine species that entered from the Gulf of California. Freshwater fishes of the lowermost reach included Colorado squawfish/charalote, bony tail/ charalito eleganti, and razorback sucker/matalote jorobado, all of which passed readily through canyon reaches, but rarely lived there. All available evidence indicates that squawfish and razorback were abundant and that bony tail was common as well. Flannelmouth sucker, woundfin, and roundtail chub also were present, but are represented by only a few specimens in early collections and must have been relatively rare. Shallow sloughs and backwaters supported desert pupfish. Roundtail chub, Yaqui 30