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The genus Helicodiscus is a significant element of theTexas cave fauna.Family OrthalicidaeAlthough seven species of the family Orthalicidaehave been reported from caves, the only one which isknown with certainty to live in caves is Bulimulusunicolor (Sowerby). This species was reported fromseveral caves in Yucatan (Bequaert and Clench, 1936,1938); it has been collected from several additionalcaves recently.Family SpiraxidaeThis is the most important family of snails withrespect to the cave ecosystem, with species of Euglandina,Spiraxis, and Streptostyla having been found astroglophiles. Euglandina cylindracea (Phillips), Streptostylameridana meridana (MoreIet), and Streptostylaventricosula (Morelet) are frequently collectedin the caves of the Yucatan Peninsula. Streptostylajilitlana Dall is an important species in the high altitudecaves of Queretaro and San Luis PotosI. Eggs,newly hatched young, and adults of Streptostylabartschi (Dall) have been found in the inner rooms ofCueva de la Mina, Tamaulipas (Reddell and Mitchell,1971b). This species is also known from other cavesin San Luis PotosI and Tamaulipas.Family UrocoptidaeBrachypodella dubia Pilsbry and Microceramusconcisus (Morelet) are frequently encountered speciesin the caves of the Yucatan Peninsula. Thompson(1967) reported Brachypodella speluncae (Pfeiffer)from two caves in El Peten, Guatemala. A new speciesof the genus Coelocentrum is known from caves inTamaulipas.Family XanthonychidaeThe only species of this family known from Mexicancaves is an undescribed species of Xanthonyxfrom Cueva de la Capilla, Tamaulipas. It was foundon the wall of the cave near a small upper entrance.Family ZonitidaeSeveral species of zonitid snail are known fromMexican caves. The only one which is common isHawaiia minuscula (Binney), known from caves inCampeche, Veracruz, and Yucatan.Class PelecypodaFew clams have ever been recorded from caves andthen usually from the vicinity of spring entrances. Asmall undetermined species is known from Cueva delNacimiento del Rio San Antonio, Oaxaca. This speciesinhabits the stream passage in large numbers andis pigmentless with a· thin shell allowing the internalorgans to be observed. The determination of itsecological status must await further study.Phylum ArthropodaClass CrustaceaThe class Crustacea is second only to the Arachnidain the number and diversity of troglobites presentin Mexican and Guatemalan caves. Of the eightorders of subterranean crustaceans represented, sixcontain troglobites (see Table 10). Two additionalorders, the Thermosbaenacea and the Bathynellacea,are present in the caves of Texas and other parts ofthe world but are not yet known from Mexico orCentral America. This lack is probably a reflectionon collecting techniques rather than an indication ofthe absence of these groups. In general the planktonTable 10.-Summary of cave inhabiting Crustacea.TroglobitesOther SpeciesBranchiuraArguloidaArgulidae 0 2CopepodaCalanoidaDiaptomidae 1 3CyclopoidaCyclopidae 0 10HarpacticoidaAmeiridae 0 5Canthocamptidae 0 2OstracodaPodocopaCypridae 0 12Darwinulidae 0 1Entocytheridae 2 10BranchipodaCladoceraChydoridae 0 1Daphnidae 0 7Malacostraca*Isopoda 40 16AmphipodaBogidiellidae 9 0Hadziidae 5 0Hyalellidae 0 1Melitidae 0 1MysidaceaLepidomysidae 2 0Mysidae 2 0*Decapoda 17 18Total 78 89*For summary by families see Tables 11-12.80