FRESHWATER FISH FAUNA 215 



cisely when antl where they or their immediate ancestors arrived lias 

 not been stated. Study of the physiographic map of Mexico pre- 

 pared by Hoy (1943) and of World Aeronautical Charts 470 (San- 

 tiago Mountains, 1950, rev. ed.) and 520 (Lake Santiaguillo, 1951, 

 rev. ed.), shows that capture of a tributary of the Rio Conchos by 

 the Rio Papigochic (of the Yaqui system) could readily have taken 

 place about 28 airline miles south of Minaca, Chihuahua. Also, 

 instead of taking the abrupt horseshoe turn that the Papigochic 

 now follows northwest of Minaca, this segment of the stream may 

 formerly have flowed northward to form the headwaters of Rio 

 Casas Grandes, a stream of interior drainage in Chihuahua. In either 

 event, Rio Grande types would have been transferred to the Yaqui 

 fauna. 



Three species, Catostomus bernardini, Agosia sp. (near chryso- 

 gaster), and Gila minacae (= G. robusta; Miller and Uyeno, manu- 

 script), are the same as or most closely allied to Colorado River 

 species, and thus indicate entry into the Yaqui from the north. The 

 2 remaining primary fishes are a sucker (Catostomus) and a minnow 

 (Gila purpurea). The former, of uncertain relationships, occurs in 

 the headwaters of both the Yaqui and the Casas Grandes, whereas 

 the latter, related to G. orcutti and G. ditaenia, inhabits the Yaqui 

 and Rio Sonora. No genera are endemic and but one species, No- 

 tropis mearnsi, scarcely distinct from N. formosus of the Rio Casas 

 Grandes, is regarded as indigenous. 



Minor Coastal Drainages 



Streams and interior springs from central Baja California north- 

 ward to San Luis Obispo Creek, California, harbor limited fish faunas 

 (arbitrarily combined in Table I). Although 12 families are repre- 

 sented, these comprise only 18 species, of which but 3 are primary 

 freshwater fishes. One of these, Rhinichthys osculus, is of little 

 zoogeographic help. Gila orcutti, with its closest relatives in northern 

 Sonora (G. ditaenia) and in the Yaqui (G. purpurea), evidently came 

 into southern California from the direction of the Colorado River. 

 The third freshwater fish, Pantosteus santaanae, is most closely re- 

 lated to species now inhabiting the Great Basin, whence it pre- 

 sumably came, perhaps in Pliocene time. 



The two secondary fishes, Fmidulus parvipinnis and F. lima, are 

 the only Pacific representatives of a genus that has its center of 



