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y the waters of the Amistad Reservoir. The cave,which consists largely of a steeply sloping passageending in a deep pool, is formed in the Salmon PeakFormation of Cretaceous age (Smith, 1970) at anelevation of 330 meters.The fauna, as is to be expected, is closely relatedto that of Texas immediately across the Rio Grande.Of the 17 species identified, two are troglobites: theagelenid spider Cicurina (Cicurella) coahuila Gertschand the cambalid milliped Cambala speobia (Chamberlin).The latter species is widespread in CentralTexas. Troglophiles include the porcellionid isopodPorcellio gertschi Van Name, the pholcid spiderPhysocyclus enaulus Crosby, a scytodid spider of thegenus Loxosceles, the collembolan Pseudosinellaviolenta (Folsom), and the carabid beetles Rhadinearaizai (Bolivar) and Tachys (Tachys) proximus Say.Basins and RangesThe Basins and Ranges province consists of an areaof folded and faulted mountain ranges separated bywide valleys and basins. The mountains are generallyoriented along a northwest-southeast axis and frequentlyenclose large closed basins (boisones). Themost notable of these is the Bolson de Mapimi inDurango, but the Bolson de Cuatro Cienegas deCarranza in Coahuila is of particular importance becauseof its rich endemic subterranean aquatic fauna.The western ranges are largely igneous, but to theeast they tend to be composed of folded Cretaceoussediments. This province extends from the southwesternUnited States into northern Durango andsouthern Coahuila. It is bounded on the west by theSierra Madre Occidental, on the east by the SierraMadre Oriental, and on the south by the Cross Rangesof the Sierra Madre Oriental. The average elevation ofthe filled basins is about 1,200 meters, with themountains rising up to several thousand meters ahovethe valleys. Russell and Raines (1967) have describedthe general geology of the Laredo-Monterrey areawith special reference to cave origins. Brand (1937)includes a concise account of the physiography andgeology of northwestern Chihuahua.Despite its proximity to the United States, thisarea has been little studied speleologically. Only sixcaves are known for the province outside of the vicinityof Cuatro Cienegas de Carranza. Most work evenin the Cuatro Cienegas de Carranza region has been inthe waters flowing into the basin itself, with the cavesin the mountains surrounding the basin remainingvirtually unknown.Salaices, Chihuahua.-This region includes severallow limestone hills in the vicinity of Salaices, a smalltown on the highway between Jimenez and Parral.The only caves known are Cueva de los Muchachos, avertical sinkhole dropping to a short horizontal passage,and Cueva del Diablo. The latter cave is an extensivemaze containing more than one kilometer ofexplored passage (Reddell, 1977a). The only faunarecorded from Cueva de los Muchachos is a species ofrhaphidophorid cricket. Cueva del Diablo is generallydry but it does contain 16 species, of which one is apossible troglobite. Cirolanid isopods found dead in alow pool remain to be rediscovered. The only apparenttroglobite is the endemic pholcid spider Psilochorusdiablo Gertsch. The troglophile fauna includesthe nesticid spider Eidmannella pallida (Emerton),the pholcid spider Physocyclus enaulus Crosby, andthe psocid Psyllipsocus ramburii Selys-Longchamps.The fauna is typical of the arid regions of northernMexico and adjacent United States.Santa Elena, Chihuahua.-This is a poorly definedregion located south of Santa Elena Canyon on theRio Grande. The only cave to be investigated withrespect to its invertebrate fauna is Sotano de Sauz,a 220-meter-deep cave with an unusually high airtemperature. A massive die-off of the bat Mormoopsmegalophylla megalophylla Peters was reported bySprouse (1977). The only probable troglophile identifiedfrom the cave is a pholcid spider of the genusPsilochorus.Cuatro Cienegas de Carranza, Coahuila.-Thisregion includes the Bolson de Cuatro Cienegas deCarranza and several ranges of mountains which surroundit. The basin is about 40 kilometers wide (eastto west) and 30 kilometers long (north to south) andis formed at an elevation of about 740 meters. Thesurrounding mountains attain elevations of more than3,000 meters. Minckley (1969) has provided an excellentsummary of the geology, hydrology, and physiographyof this region. The deposits in the closedbasin include alluvium, detrital deposits from themountains, and gypsum (mostly in the form of sandor gypsite). Drainage in the basin is almost entirelysubterranean and water rising from deep sourcesalong the bases of the mountains either emerges assprings or flows underground through solution channels.Collapse of the poorly consolidated gypsite andother deposits allows access to these subterraneanstreams through the means of shallow natural wellsor lagunas. The surrounding mountains are formedlargely of Cretaceous limestone.Only five caves have been investigated in thisregion. One of these, Cueva de San Vicente, is locatedin the Sierra de San Vicente to the east of the basin,while the remaining four occur in Canon del Pedregosoin the Sierra de San Marcos to the west of the23