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Discussion.-This large, troglobitic flatworm issimilar to O. mexicana in many respects but is morethan twice as long. Since the dimarcusid planariansbelong to the Maricola, a primarily marine group, thediscovery of this relict species at 2,115 meters in elevationis very interesting. Marine relict species at altitudesin excess of 1,000 meters are rare, but in Mexicothey include Mexicerberus troglodytes Schultzand Speocirolana pelaezi Bolivar in the caves of theSierra de Guatemala, Tamaulipas.Opisthobursa mexicana BenazziTurbelarido cavemicola: Villalobos, 1960:332.Opisthobursa mexicana Benazzi, 1972:405; Mitchelland Kawakatsu, 1972:16; Benazzi, 1973:133-134;Benazzi and Giannini, 1974:47-54, fig. 3, pI. 1-4;Sbordoni, 1974:366; Sbordoni et al., 1974:14, 15;Benazzi, 1976:533, 535; Ball, 1977a:150, 153,154; Ball, 1977b:27, 29, 32.Dimarcus villalobosi Mitchell and Kawakatsu, 1972:2-15, fig. 1-13; Benazzi, 1973:133, 134; Mitchelland Kawakatsu, 1973a:640, 642; Mitchell and Kawakatsu,1973b:168, 169; Reddell, 1973a:32, 37;Benazzi and Giannini, 1974:54; Kawakatsu, 1975:7, fig. 2; Benazzi, 1976:533; Kawakatsu, 1976:36.Opisthobursa: Ball, 1976:649.Opisthobursa (part): Ball, 1977a:154; Ball, 1977b:27,29, fig. 1,3.Type-locality.-Of Opisthobursa mexicana: Grutasde Cocona, Tabasco, Mexico; of Dimarcus villalobosi:Las Grutas de Cocona, Teapa, Tabasco, Mexico.Distribution.-Known only from the type-locality.See Fig. 3.Discussion.-This species is believed by Mitchelland Kawakatsu (1972) to be a true marine relict. Itsrelationship to other species of Maricola is obscureand so distant as to have necessitated the erection ofa new family to include it. Ball (1977a; 1977b) hasdiscussed the status and relationships of the familyand considers it to be a very primitive group. Thespecies has been found in small travertine pools.Suborder PaludicolaFamily DugesiidaeThe family Dugesiidae is represented in the cavesof Mexico by three described troglobites and onetroglophile (see Fig. 3). In addition, troglophilic andtroglobitic Dugesia have been found in caves in SanLuis Potosi, Tabasco, Tamaulipas, Veracruz, and Yucatan.This material, together with many related epigeanspecimens, is now under study by M. Kawakatsuand R. W. Mitchell. It is interesting that the Mexicanpaludicolan flatworms belong to the Dugesiidae ratherthan to the Planariidae or Kenkiidae. The lattertwo families predominate in the cave fauna of theUnited States and include numerous troglobites. NoDugesia is known as a troglobite in the United Statesalthough a few populations are troglophiles in Texasand probably elsewhere.Dugesia barbarae Mitchell and KawakatsuDugesia sp. II: Reddell and Mitchell, 1971b: 182;Reddell and Elliott, 1973b:182.Dugesia barbarae Mitchell and Kawakatsu, 1973a:641, 646-649, 662, 663, 661-671, 673, 675, fig.4-5, 10, 15, 28-30; Mitchell and Kawakatsu,1973b:168-169; Reddell and Elliott, 1973b:181,182; Kenk, 1974:22,28; Kenk, 1975:113; Kawakatsu,1976:36.Dugesia (part): Reddell, 1973a:32.Type-locality.-La Cueva de la Capilla, Municipiode Jaumave, Tamaulipas, Mexico.Distribution.-Known only from the type-locality.See Fig. 3.Discussion.-This species is closely related to D.typhlomexicana. It is known only from small drippools in the terminal room of this cave. A troglophilicflatworm, probably D. guatemalensis Mitchell andKawakatsu, inhabits larger silt-floored pools in thesame room. The evolution of D. barbarae has beendiscussed by Mitchell and Kawakatsu (1973a). Theypostulate that the ancestor of this species and D.typhlomexicana invaded caves in the Sierra de Guatemalaearly in the Pleistocene. With the colder climateof the glacials, the surface ancestor was eliminatedfrom higher elevations and the cave species evolved.The presence in these caves of the troglophilic D. guatemalensisis explained by postulating a re-invasion ofthe area by Dugesia from the north.Dugesia mckenziei Mitchell and KawakatsuDugesia mckenziei Mitchell and Kawakatsu, 1973b:165-170, fig. 1-10; Kenk, 1974:26; Kenk, 1975:113; Kawakatsu; 1976:36.Dugesia mackenziei: Kawakatsu, 1977:18 (erroneousspelling).Type-Iocality.-La Cueva de Los Llanos, 15 kmESE San Cristobal de las Casas, Chiapas, Mexico.Distribution.-Known only from two caves at LosLlanos, Chiapas. See Fig. 3.Records.-Chiapas: Cueva de Los Llanos andCueva de los MurcieIagos.72