A revision of the Mexican cyprinid fish genus Algansea

" The cyprinid fishes of the New World range southward only a short distance into Middle America, reaching their southern limit to the west and northwest of the Isthmus of Tehuantepec in southern Mexico. Along the Atlantic slope a few species extend into the tropics with one (Dionda ipni) ranging as far south as the Rio Misantla (at 20" N lat.) in Veracruz (Hubbs and Miller, 1977). On the highlands of the Atlantic slope they occur as far south as certain tributaries of the Rio Papaloapan in Oaxaca (De Buen, 1955). On the Pacific side of Mixico cyprinids reach the Rio Verde basin (16" 31' N lat.) to the east of the Rio Balsas drainage in Oaxaca (Cortis, 1968). As one progresses southward from the United States border on the Mexican Plateau, the number of genera and species decreases rapidly. In the large Rio Lerma basin (near 20" N lat.), only three genera remain: Algansea, Notropis, and Yuriria. Algansea is found throughout the Rio Lerma and contiguous areas (Figs. 1-2), with a distribution resembling that of the atherinid genus Chirostoma (Barbour, 1973a, b) and, to a lesser extent, that of the Goodeidae (Hubbs and Turner, 1939; Miller and Fitzsimons, 1971).

The genus Algansea, when described by Girard (1856), included three nominal species of Siphateles, which is now regarded as a subgenus of Gila (see Miller, 1968). The type-species, Leuciscus tincella Valenciennes, was designated by Jordan and Gilbert (1 883). Jordan and Snyder (1900) erected the monotypic genus Xystrosus for a lacustrine-adapted cyprinid from Lake Chapala, Jalisco-Michoacgn. Algansea antica Cope (syntypes, ANSP 4911-13, 16868, examined by R.R.M.), said to have come from Texas, is a synonym of Gila bicolor (subgenus Siphateles), and probably came from Nevada or an adjacent state (Fowler, 1913:69). We recognize six species within Algansea, of which one is described herein, including the nominal Xystrosus popoche. Our objectives are to clarify the systematics of Algansea and to discuss the evolution of the species. It is clear from this study that Algansea is very closely related to certain species of the genus Gila. As it is beyond the scope of this paper to revise that genus as well as Algansea, we have left any possible taxonomic changes involving the species of both groups to future workers "