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fonned in Cretaceous limestone of the EI Abra Formation.The large caves are characterized by considerablevertical development with two (Hoya de lasConchas and Sotano de Nogal) being more than 500meters deep. Elevations range from 1,000 to 1,500meters, with most of the caves occurring at about1,400 meters. Drainage is almost entirely internal andmany of the caves receive considerable runoff.Of the 18 species detennined from the caves of theregion, the only troglobite is an unidentified isopodof the family Trichoniscidae. The remainder of thefauna is typical of the Sierra Madre Oriental and includesthe nesticid spider Eidmannella pallida (Emerton),the opilionid Hoplobunus sp., the centipedeNewportia n. sp., the collembolan Pseudosinellareddelli Christiansen, and the gryllid cricket Paracophussp.Tancoyol, Queretaro.-This region is located immediatelywest of the Xilitla Plateau. Little is knownabout the region, but karst development includeslarge dolinas and sinkholes. The largest cave in theregion is the largely vertical EI Socavon, whichattains a depth of about 200 meters.Only five species have been reported from thethree caves that have been biologically investigated.The only troglobite is the opilionid Hoplobunusqueretarius Silhavy, also known from the LagunaColorado region to the south. Troglophiles includean agelenid spider of the genus Tegenaria, a ctenidspider of the genus Ctenus, and a pholcid spider ofthe genus Physocyclus.Xilitla Plateau, Queretaro and San Luis Potosi.­ThiS region includes an area of high elevation karstlying north of Xilitla and including parts of the statesof Queretaro and San Luis PotosI. No collectionshave yet been made in the San Luis Potosi part ofthe region. Fish (1978; 1979) has discussed thegeology, physiography, and caves of the region. Thecaves are fonned in the Cretaceous El Abra Limestone,and there is extensive karst development, withdolinas, sinkholes, pinnacles, and lapiez present.Elevations range from about 1,500 to 2,900 meters.Although a few deep caves occur, such as the 559­meter-deep Sotano de Trinidad, the three caves whichhave been biologically investigated are relatively horizontal.Much of the fauna from this region awaits study,but 19 species, of which four are troglobites, havebeen identified. The troglobites include trichoniscidisopods, the diplurid spider Euagrus n. sp., the opilionidHoplobunus sp., and the rhachodesmid millipedUnculabes crispus Causey. The last species is alsoknown from the Xilitla region to the south, and theothers have their closest affinities with that region.The troglophile fauna includes flatwonns of thegenus Dugesia; the agelenid spider Tegenaria selvaRoth; the nesticid spiders Eidmannella pallida (Emerton),Gaucelmus augustinus Keyserling, and two undescribedspecies of the genus Nesticus; the opilionidKaros depressus Goodnight and Goodnight; and thecarabid beetle Platynus (Mexisphodrus) sp.Aquismon, San Luis Potosi.-This region is locatedwest of the town of Aquism6n and extends from theXilitla Plateau north for about 20 kilometers; it isbounded on the west by the Rio Santa Maria. Elevationsrange from about 400 to 1,000 meters. Karstdevelopment in the region is spectacular in places,with large deep dolinas, huge sinkholes, karren, andhaystack hills. Most of the drainage is subterraneanand several caves receive considerable floodwater.Caves range from small pits and shallow horizontalpassages to enonnous vertical shafts such as Hoya delas Guaguas and Sotano de las Golondrinas. The principallimestoneunit in the region is the EI Abra (=EIDoctor) Fonnation. Raines (1968) includes a discussionof the geology and physiography.A total of 57 species, of which 10 are troglobites,has been reported from the 15 caves studied. Theonly aquatic troglobites are the cirolanid isopodsSpeocirolana bolivari (Rioja) and S. pelaezi (Bolivar).Terrestrial troglobites, all of which are typical elementsof this general area, include the trichoniscidisopod Mexiconiscus laevis (Rioja); the amblypygidParaphrynus velmae Mullinex; the opilionid Hoplobunusplanus Goodnight and Goodnight; the glomeridmilliped Glomeroides sp.; the trichopetalidmilliped Mexiterpes fishi (Causey); the rhachodesmidmilliped Unculabes criJpus Causey; the cambalidmilliped Mexicambala russelli Causey; and the gryllidcricket Paracophus cladonotus Hubbell. Except forH. planus and M. fishi all of these species are alsoknown from the Xilitla region.The troglophile fauna includes flatwonns of thegenus Dugesia; the crayfish Procambarus (Ortmannicus)toltecae Hobbs; the spiders Ctenus mitchelliGertsch, Gaucelmus sp., and Metagonia sp.; therhachodesmid millipeds Strongylodesmus sp. andUnculabes columbinus Causey; the collembolanPseudosinella sp.; the gryllid cricket Paracophusplaconotus Hubbell; carabid beetles of the generaArdistomis and Tachys; and the leiodid beetles Dissochaetussp. and Proptomaphaginus microps Peck.Cerro de la Cochina, San Luis Potosi.-This is asmall limestone range located west of Matehuala. Theonly cave studied is Cueva del Cochino, a dry horizontalcave located at an elevation of 1,560 meters.No troglobites are known from the region and the32