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Family TrichodactylidaeTwo species of the family Trichodactylidae havebeen reported from Mexican caves. Bott (1969) describedTrichodactylus (Rodriguezia) bidens fromCueva del Azufre, Tabasco. This is an eyed speciesand presumably a troglophile. The other species is atroglobite and is discussed below.Trichodactylus (Rodriguezia) mensabak Cottarelliand ArganoTrichodactylus (Rodriguezia) mensabak Cottarelliand Argano, 1977:207-212, fig. 1·2; Sbordoni etaI., 1977:74, pI. lIB (nomen nudum).Trichodactylus mensabak: Sbordoni et al., 1977:37(nomen nudum).Type-Iocality.-Cueva de Nicolas Bravo, 'fila, Chiapas,Mexico.Distribution.-Known only from the type-locality_See Fig. 16.Discussion.-This is the only known troglobiticcrab in the family Trichodactylidae. It is most closelyrelated to T. (R.) vil/alobosi Rodriguez and Manrique,an epigean species from Chiapas.Class ArachnidaThe class Arachnida has been the most successfulof all groups which have invaded the cave habitat inMexico and Central America. A total of 122 speciesof troglobite is known from Mexi,;o, Guatemala, andBelize, and another 420 species have been iden tifiedas troglophiles, trogloxenes, or accidentals. Mexico isunique in that all 11 orders of arachnid have been collectedin caves (see Table 13)_ The orders Scorpiones,Pseudoscorpionida, Schizomida, Amblypygida, Araneae,Ricinulei, Opilionida, and Acarina contain troglobites.Order ScorpionesThe order Scorpiones is generally poorly representedin the fauna of caves. The European l1elisaurusxambeui Simon is frequently found in caves but alsoinhabits deep soil and litter. Uroctonus sequoiaGertsch and Soleglad and Vaejovis iviei Gertsch andSoleglad, both from California, and V. reddelliGertsch and Soleglad from Texas are troglophileswhich show little or no adaptation to a cavernicoleexistence. Only eight described species are consideredto be significantly cave adapted, of which seven occurin Mexico. Uroctonus grahami Gertsch and Solegladfrom Samwell Cave, California, is probably a troglobitealthough it retains vestiges of eyes (Gertsch andTable 13.-Summary of cave inhabiting Arachnida.TroglobitesOther SpeciesScorpionesUnknown family 1 0Buthidae 0 2Chactidae 5 1Diplocentridae 3 2Vaejovidae 1 2*Pseudoscorpionida 24 17UropygidaThelyphonidae 0 1SchizomidaeProtoschizomidae 3 0Schizomidae 12 12AmblypygidaCharontidae 1 0Phrynidae 5 7*Araneae 47 252RicinuleiRicinoididae 3 6*Opilionida 15 35PalpigradidaEukoeninlid ae 0 ISolpugida 0 1*Acarina 2 81Total 122 420*-For summary by families see Tables 14-17.Soleglad, 1972). The troglobitic scorpion fauna ofMexico includes three described and two undescribedchactids, three diplocentrids, one vaejovid, and a remarkableeyeless species from Oaxaca of unknownfamilial relationship.Family ButhidaeCentruroides yucatanus (Chamberlin and Ivie) wasdescribed from Actun Loltun, Yucatan (Chamberlinand lvie, 1938a), but is a junior synonym of C. ochraceousPocock, which has been collected from underrocks in the entrance area of two caves and fromdarkness in two other caves in Yucatan (Wagner,1977). Centruroides gracilis (Latreille) has beenfound in Cueva del Salitre, San Luis PotosI, andCueva de los Cuarteles, Tamaulipas. In the latter cavea single large specimen was collected from the ceilingof thc cave in total darkness.Family ChactidaeThe family Chactidae is represented in Mexicancaves by the three troglobites of the genus Typhlochactasdiscussed below, by an undescribed genuswith two new troglobitic species from caves in SanLuis Potosi and Tamaulipas, and by a single speciesof possible troglophile. The last species, Megacormusgertschi Diaz Najera, has been found in two caves inQueretaro.114