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Rio Soto la Marina and terminates a short distancesouth of Aldama. Although narrow in the northernpart it widens to about 60 kilometers in the south.The highest peaks approach 1,400 meters in elevation.The principal cavernous rock unit is the TamaulipasLimestone (Muir, 1936). Martin et aI. (1954)have discussed the Sierra de Tamaulipas with respectto geology, climate, vegetation, and vertebrate fauna.The only caves that have been studied in the region arelocated at low elevations along the eastern side of therange. Nothing is known of the karst features or cavepotential of high elevations, although a few caveshave been reported by vertebrate biologists. Twocaves were visited about 50 kilometers southwest ofSoto la Marina, approximately midway in the range.One of these is a resurgence cave, but neither is verylarge. The third known cave is Cueva de los Cuartelesnear Aldanla in the extreme southern part of therange. This is a large, horizontal cave with manyentrances and more than one kilometer of passage.One part of the cave contains a large bat population,while another area consists of a single major passageinterrupted along its length by numerous large skylightentrances. A sizable spring is located near thecave and it is likely that Cueva de los Cuarteles is afossil resurgence.Despite our general paucity of knowledge of theinvertebrate fauna of the region 45 species, of whichfour are troglobites, have been thus far identified.The troglobitic fauna includes the cirolanid isopodSpeocirolana pelaezi (Bolivar) and its entocytheridostracod associate, Sphaeromicola cirolanae Rioja.These species are also known from caves in SanLuis Potosi and Tamaulipas in the Sierra MadreOriental. The remaining tw~ troglobites are schizomids,Schizomus lukensi Rowland and an undescribedspecies of Schizomus. Both are closelyrelated to species in the Sierra de EI Abra and Sierrade Guatemala and presumably represent relicts of awidespread species ancestral to species in all threeregions. The terrestrial troglophile fauna is alsoclosely related to the fauna of the Sierra MadreOriental, with some species occurring in both regions.Three arachnids are endemic to the caves of theSierra de Tamaulipas: the pholcid spiders Pholcophorabolivari Gertsch and P. mitchelli Gertschand the opilionid Stygnomma tuberculata Goodnightand Goodnight. Other species of interest include theamblypygid Paraphrynus pococki Mullinex, the ctenidspider Ctenus mitchelli Gertsch, the mysmenidspider ,vJaymena chica Gertsch, the nesticid spiderGaucelmus augustinus Keyserling, the pholcid spiderModisimus texanus Banks, the scytodid spider Loxoscelesdevia Gertsch and !Vlulaik, and the collembolansPseudosinella violenta (Folsom) and Acherontiellasabina Bonet.Neovolcanic PlateauThe Neovolcanic Plateau forms a great band acrosscentral Mexico from the Pacific coast in J alisco to theGulf of Mexico east of Jalapa, Veracruz. Hundreds ofvolcanos, most now extinct, rise from a comparativelylevel plain formed by ash and lava deposits.Two volcanos, J orullo and Paricutin, have erupted inrecent times and an eruption south of Mexico Citycovered prehistoric settlements in the Pedregal de SanAngel. A chain of large peaks, including Tancitaro,Toluca, Popocatepetl, Malinche, Orizaba, and Cofrede Perote, dominates the landscape. The average elevationin this province is above 2,500 meters, withOrizaba rising to 5,747 meters above sea level. In afew areas erosion has exposed older sedimentaryrocks, some of which are known to be cavernous.. 'one of these inliers have been investigated for caves.Lava tubes are abundant throughout much of thearea, but they have been little studied speleologically.Caves on the slopes of Cerro Xictle to the south ofMexico City have been studied with respect to theirbat and associated ectoparasitic fauna, but generalinvertebrate collections have not been made. Onecave on Cerro de la Estrella to the east of MexicoCity has been visited and others are known to exist.Two caves on the slopes of Cofre de Perote have beenexamined with collections made in one. A third cavenear Jalapa has been studied, and three caves near thetown of Buena Vista have been visited. The presenceof troglohites in the caves on Cerro de la Estrella andCofre de Perote indicates the existence of a potentiallyrich cavernicole fauna on the Neovolcanic Plateau.Cerro de la Estrella, Distrito Federal.~This smallpeak is located south of Tapijutapa on the easternedge of Mexico City. It is formed of Pliocene volcanicdeposits (Schlaepfer, 1968). One cave has beenbiologically investigated, but other larger ones arereported. This cave is generally dry and heavily pollutedwith trash and human feces. Of eight speciesidentified from the cave, an undetermined genus andspecies of nicoletiid thysanuran is the only possibletroglobite. The troglophilic fauna includes the nesticidspider Eidmannella pallida (Emerton) and anundescribed species of the pholcid genus Coryssocnemis.Buena Vista, Veracruz.-This is an ill-definedregion in the immediate vicinity of the town ofBuena Vista. Three caves, none very well-suited forcavernicoles, have been studied. One cave is small,horizontal, and of little interest; the second, Cuevade Cantil Blanco, consists of a single 80.meter.long39