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only in one cave in the Coastal Plain of Yucatan; O.zizicolens (Chamberlin) appears to be restricted tocaves in the Sierra de Ticul, Yucatan.The collembolan family Entomobryidae includesseveral genera with cave representatives, but the mostimportant by far is Pseudosinella. This widely distributedgenus contains troglobitic species in Alta Verapaz,Guatemala, and Oaxaca and Tamaulipas, Mexico.The genus is now under revision, and more meaningfuldata on its distribution in Mexico and CentralAmerica should be forthcoming.One of the more important beetle families to inhabitcaves in North America is the Leiodidae. Numerousspecies of this family have invaded Mexican andCentral American caves, but only two troglobiteshave been described. These two species, Ptomaphagus(Adelops) troglomexicanus Peck from the Sierra deGuatemala and P. (A.) mckenziei Peck from the Purificacionregion of Tamaulipas and Nuevo Leon, areboth restricted to high elevations.As is apparent from the above, the terrestrial troglobitefauna of Mexico and Central America includesan assortment of species derived from ancestors witha variety of affinities. Perhaps one of the moreinteresting aspects of the fauna of this region is theadmixture of temperate and tropical derivatives inthe same caves. This alone is a good indication of thecomplexity of the past history of the region. Speciesderived from ancestors adapted for colder climatesnow coexist in the same caves with species derivedfrom those adapted for wamler climates.Also of no slight interest is the existence of numeroustroglobites in caves in areas of lowland tropicalforests. It has been one of the axioms of modembiospeleology (Vandel, 1964; \Iitchell, 1969a) thatterrestrial troglobites are rare in tropical regions. Thepresence of a rich troglobitic fauna at high elevationscan be readily explained by the model of Barr (I968a)in which past climatic changes extirpated the epigeanfauna, allowing for divergence to occur in the cavemicolepopulations of that fauna. Climatic fluctuationsduring the Pleistocene, though presumably less severein Mexico and Central America, certainly were feltat higher elevations and may have allowed for theextinction of the surface ancestors of the present-daytroglobites. The existence of a rich troglobitic faunaat lower elevations in tropical regions is now uncontested.Not only do we have a rich fauna in lowlandparts of Mexico and Central America, but studies byHowarth (1973) in Hawaii, and by Peck (1976) inJamaica and other islands of the West Indies provethe existence of a rich tropical troglobite fauna inother areas as well. Only with much additional study,both of existing collections and in under-investigatedareas, can a really comprehensive model be proposedfor the evolution of this fauna. It is possible, however,that the Pleistocene climatic fluctuations werefelt sufficiently at lower elevations to cause the extinctionof surface populations of many groups insome karst regions. The more vagile species, such asbeetles, were able to repopulate the areas beforedivergence occurred, while groups such as millipeds,isopods, and the smaller arachnids had time to becomegenetically isolated from the re-invading stock.The preponderance of the smaller, more delicatespecies in lowland tropical caves would seem to givecredence to this hypothesis.Terrestrial TroglophilesThe terrestrial troglophile fauna of Mexico, Guatemala,and Belize contains both species which areabundant on the surface and species known onlyfrom caves. Some of the latter may eventually proveto be cave restricted, although they do not yet exhibitthe reduction or loss of eyes and pigmentation tobe found in the troglobites. Other species known onlyfrom caves belong to groups of endogean forms inwhich eyes are absent and pigmentation reduced. Thepresent brief discussion of Mexican troglophiles willoutline the various groups of troglophiles withrespect to their general distribution. For furtherdetails on the distrihu tion of the more importantspecies, see the Systematic Review section whichfollows.A few species which are troglophilic in caves inthis region have extremely wide ranges. Among these,mention may be made of the nesticid spiders Gaucelmusaugustinus Keyserling and Eidmannella pallida(Emerton). These two species are important membersof the cavemicole communities of the United States,Mexico, and Central America. The preponderance ofrecords for the two species in caves in many areasreflects both a predilection for the cavernicole habitatand a bias towards cave collections. One other exampleof wide distribution should suffice here. Thisis that of the leiodid beetles of the genus Dissochaetus.Some species of this genus range from SouthAmerica into northern Mexico. Although cave recordsfor the southern part of the range are rare (as arecollections), numerous troglophile populations occurin Mexico, Guatemala, and Belize.Many species with more limited ranges will befound in caves wherever they are available. This isespecially true of the more mesic-adapted forms,such as many millipeds, isopods, arachnids, and softbodiedinsects. Examples include various species ofarmadillid and porcellionid isopod, rhachodesmid67