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described, the genus occurs in caves from Nuevo Leoninto Guatemala The known distributions of the speciesare quite limited but will doubtless be found tobe much wider with study of unidentified material.All species of the genus known from Mexico are troglobites,as are two species found in Texas caves. Theonly epigean species of the genus is B. heroldi (Arcangeli)from caves and surface localities in California.The troglobitic species occur from low to high elevationsand presumably represent a relict of a widespreadfauna that ranged thoughout the western andsouthwestern United States into Central America buthas now become extinct on the surface, except in themountains of California.Another group which is probably a relict of aonce-widespread temperate fauna is the scorpiongenus Typhlochactas. This genus includes three describedtroglobites from caves in Veracruz, San LuisPotosi, and Tamaulipas, and a litter-inhabitingspecies from high elevation forests in Oaxaca. As insome other groups, the most highly cave-adaptedspecies occurs in low elevations. The evolution anddistribution of Typhlochactas are discussed in moredetail in the Systematic Review below.Knowledge of the pseudoscorpion fauna of Mexico,both cave and epigean, is very limited, but the chthoniidgenus Aphrastochthonius would appear to be amember of a group with significant temperate affinities.Four troglobites in this genus have been describedfrom this region, each known only from thetype-locality. These occur in Tamaulipas, San LuisPotosi, and Alta Verapaz, Guatemala. Other troglobitesin the genus have been found in Alabama, NewMexico, and Cuba. One epigean species has beendescribed from leaf litter in Chiapas.Agelenid spiders of the genus Tegenaria are animportant element of the cavernicole fauna of Mexico.This genus is frequently collected on the surface inthe United States, but appears to be rare in caves outsideof Mexico, where two troglobites and seven troglophileshave been described.The family Leptonetidae is a largely Nearcticgroup containing numerous troglobites and troglophilesin the caves of the United States and Mexico.With the exception of a few epigean species, mostof the records for this family south of the UnitedStates are from caves. This may reflect a bias forcave collections, but nevertheless the group as awhole is certainly aligned with the Nearctic fauna.Troglobites have been collected from caves in theSierra Madre Oriental from Tamaulipas, Queretaro,and Nuevo Leon. One species, Leptoneta limpidaGertsch from Cueva de los Riscos, Durango, is mostclosely related to species from Texas caves and isnow a relict isolated by the surrounding desert.Although some species of the spider family Nesticidaerange widely throughout North America wellinto Central America; the family has reached itsgreatest degree of radiation in Nearctic regions. Thegenus Nesticus is unknown from the surface inMexico and includes troglobites from Veracruz,Tamaulipas, Nuevo Leon, and Puebta.Species with tropical affinities.-The vast majorityof the cavernicole fauna of Mexico is made up ofNeotropical elements. In some instances all or mostof the species in these groups known from Mexico,Guatemala, and Belize are trog[ohites, but in mostcases there are closely relakd taxa both on the surfaceand underground. It i~ not possible to do morehere than to mention SOIlIl' of the more significantspecies and briefly ou tlin.: di~lribll tiona} patterns asthey are presently known.Two families of lIIilliped which include troglobitesreach their northern distributional limit in southernMexico. The Glomeridesmidal' ranges from Panamainto Mexico south of the Isthmus of Tehuantepec.The only Mexican species is the troglohite Clomeridesmussbordonii Shear from caws in Chiapas andTabasco. With the exception of one .:pii(ean species inTabasco, the family OniscodeslIIidat· is represented inMexico only by two troglobites in YCraITIlZ: Bonetesmusojo Shear from the Orizaba region and B. verusChamberlin from the Atoyac region.Two species of philosciid isopod are troglobitesin Mexican and Guatemalan caves; both helong togenera known only from the tropics. Colombophilosciacavernicola Vandel was described frolll caves inVenezuela and has since been reported by Schultz(1977) from a cave in Huehuetenango, Guatemala.Even if this species proves to be an undescribed one,it is obviously a tropical element and one of the fewhaving close affinities with the South Americanfauna. The only other species of the genus occur inEcuador and the Galapagos Islands. The other troglobiticphilosciid known from this region is Troglophiloscialaevis Schultz from a cave in Yucatan; theonly other species of the genus is a Cuban troglobite.Several tropical groups include species of troglobitein more northern Mexico, but which are otherwisenot found on the surface outside of southernMexico. Included among these is the sphaeroniscidisopod Spherarmadillo cavernicola Mulaik from cavesin the Sierra de El Abra and Sierra de Guatemala.This genus and its relatives are not found on the surfacenorth of Veracruz. The squamiferid isopodgenus Trichorhina includes epigean and cavernicolespecies in Mexico and Cuba. Three troglobites andone troglophile are known. The troglophile has been64