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the pholcid spiders Metagonia maya Chamberlin andIvie, M. yucatana Chamberlin and Ivie, and Pholcophoraspeophila (Chamberlin and Ivie); the scytodidspider Loxosceles yucatana Chamberlin and Ivie;the opilionid Erginulus bimaculata Goodnight andGoodnight; pyrgodesmid millipeds of the generaCalymmodesmus and Synoptura; rhachodesmid millipedsof the genus Aceratophallus; the spirostreptidmilliped Orthoporus solicolens Chamberlin; theleiodid beetles Dissochaetus hetschkoi Reitter andPtomaphagus (Adelops) tabascensis Sbordoni; scydmaenidbeetles of the genus Euconnus (Napochus);and the ant Paratrechina pearsei (Wheeler).Sierra de Ticul, Yucatan.-The Sierra de Ticul risesabruptly from the coastal plain in southern Yucatannear its border with Carnpeche. Elevations range from70 meters in the north to about 100 meters in thesouth. The only rocks cropping out in the region areundifferentiated limestone units of Eocene or Paleoceneage. Karst development is limited to caves andminor surface features, such as shallow solutionalweathering. The Sierra de Ticul is made up of twonarrow ridges separated by a shallow valley. Caves inthe first ridge receive no significant run-off and tendto have large collapse sinkholes dropping into largerooms. Some of the larger caves, such as Actun Xpukil,contain several large rooms connected by narrowpassages. Others, such as Actun Loltlin and ActlinSabaca, have long, linear passages. Caves in the secondridge tend to be entered by small vertical or nearverticalpits, some dropping more than 30 meters.Larger caves, such as ActUn Chac, usually consist ofsingle passages gradually descending to water. A fewof the caves in this part of the range receive considerablefloodwater.The fauna of the Sierra de Ticul is very wellknown with 290 species, including 17 troglobites,identified from the 41 caves studied. The aquatictroglobite fauna includes the cirolanid isopod Creaseriellaanops (Creaser), the atyid shrimp Typhlatyapearsei Creaser, and the palaemonid shrimp Creaseriamorleyi (Creaser). The two shrimp are known fromall parts of the Peninsula, while the isopod is alsoknown from the Coastal Plain. The terrestrial troglobitefauna includes species endemic to the Sierra deTicul and species found in other parts of the Peninsula.The endemic species are the philosciid isopodTroglophiloscia laevis Schultz, the scorpion Diplocentrusanophthalmus Francke, the vachoniid pseudoscorpionsVachonium boneti Chamberlin and V.cryptum Muchmore, the amblypygid Paraphrynusreddelli Mullinex, the agelenid spider Cicurina (Cicurella)maya Gertsch, the spirostrcptid milliped Orthoporuszizicolens (Chamberlin), and the collembolanMetasinella falcifera (Mills). Species shared with theCoastal Plain are the squamiferid isopod Trichorhinapearsei (Creaser), the amblypygid Paraphrynus chacmool(Rowland), the collembolans Cyphoderusinnominatus Mills and Troglopodetes maya (Mills),and the gryllid cricket Tohila atelomma Hubbell. Theonly other troglobite is an undetermined species ofmilliped of the family Trichopolydesmidae.The only aquatic troglophiles are the copepodsMesocyclops ellipticus Kiefer, Paracyclops fimbriatus(Fischer), and Diaptomus texensis M. S. Wilson.The terrestrial troglophile fauna contains about 79species, of which some are endemic to the Sierra deTicul. These include the diplocentrid scorpion Diplocentrusreddelli Francke, the syarinid pseudoscorpionPachychitra maya Chamberlin, the oonopid spiderOonops mitchelli Gertsch, the pholcid spider Pholcophoramaria Gertsch, and the rhachodesmid millipedsAceratophallus calcehtokanus Chamberlin andA. oxkutzcabus Chamberlin. Troglophiles restrictedto the Yucatan Peninsula are the acanthodrilid earthwormsBalanteodrilus pearsei Pickford and Eodrilusoxkutzcabensis Pickford; the c1ubionid spider Tixcocobamaya Gertsch; the oonopid spider Oonopsreddelli Gertsch; the pholcid spiders Metagonia ivieiGertsch, M. maya Chamberlin and Ivie, and M. yucatanaChamberlin and Ivie; the ricinuleid Cryptocelluspearsei Chamberlin and Ivie; the chelodesmid millipedChondrodesmus sabachanus Chamberlin; the pyrgodesmidmilliped Calymmodesmus viabilis (Chamberlin):the spirostreptid milliped Orthoporus solicolensChamberlin; the collembolan Lepidocyrtus pearseiMills; the ant lion Eremeleon longior Banks; and theant Paratrechina pearsei (Wheeler). Among the moreinteresting troglophiles with a wider distribution arethe cyclophorid snail Neocyclotus dysoni berendti(Pfeiffer); the pomatiid snail Choanapoma largillierti(Pfeiffer); the spiraxid snails Euglandina cylindracea(Phillips). Streptostyla meridana meridana (Morelet),and S. ventricosula (Morelet); the schizomid Schizomusportoricensis (Chamberlin); the amblypygidParaphrynus raptator (Pocock); the mysmenid spiderMaymena mayana (Chamberlin and Ivie); the nesticidspider Eidmannella pallida (Emerton); the scytodidspider Loxosceles yucatana Chamberlin and Ivie; thetetrablemmid spider Matta sbordonii (Brignoli); andthe leiodid beetles Dissochaetus hetschkoi Reitter andPtomaphagus (Adelops) tabascensis Sbordoni.Coastal Plain, Campeche, Quintana Roo, andYucatim.-The Coastal Plain of the Yucatan Peninsulaincludes all of the state of Quintana Roo, all of Yucatanexcept for the Sierra de Ticul, and a narrow stripalong the northwest coast of Campeche. Reddell(1977b) recognizes four subdivisions: the Coastal57