PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 109(1):10-16. 1996 Identity and taxonomic status of the Mexican garter snake Thamnophis vicinus Smith, 1942 (Reptilia: Serpentes: Natricidae) Douglas A. Rossman Museum of Natural Science, Louisiana State University, Baton Rouge, Louisiana 70803, U.S.A. Abstract. — The nominal garter snake species Thamnophis vicinus is shown to be a localized color pattern morph of the wide-ranging T. cyrtopsis collaris; this morph is known to occur only in three populations in the Mexican state of Michoacan. Thamnophis vicinus was originally de-scribed (Smith 1942) from the vicinity of Morelia, Michoacan, on the basis of ten specimens differing from T. cyrtopsis only in lacking a vertebral stripe and in having large dorsal spots arranged in three rows rather than four. Bogert & Oliver (1945), Milstead (1953), Duellman (1961), and Webb (1966) concluded that T. vicinus is merely a color pattern morph of T. cyrtopsis (specifically of T. cyrtopsis collaris in the current taxonomy) and not a distinct spe-cies. However, Webb (1978) reexamined most of the type series of T. vicinus, and six additional specimens from other areas in Michoacan that combined pattern fea-tures of T. vicinus and T. cyrtopsis collaris. He concluded that the taxonomic status of T. vicinus is uncertain; for that reason, he tentatively resurrected T. vicinus as a sep-arate species. Materials and Methods Preserved specimens were borrowed from the: American Museum of Natural History (AMNH); California Academy of Sciences (CAS); private collection of E. A. Liner (EAL); Field Museum of Natural His-tory (FMNH); University of Kansas Mu-seum of Natural History (KU); Los Angeles County Museum of Natural History (LACM); Louisiana State University Mu-seum of Natural Science (LSUMZ); Muse-um of Comparative Zoology, Harvard Uni-versity (MCZ); Michigan State University Museum (MSU); Texas Cooperative Wild-life Collection, Texas A&M University (TCWC); Florida Museum of Natural His-tory, University of Florida (UF); University of Illinois Museum of Natural History (UIMNH); University of Michigan Muse-um of Zoology (UMMZ); and Collection of Vertebrates, University of Texas at Arling-ton (UTA). Four standard characters (num-bers of ventrals, subcaudals, and maxillary teeth; relative tail length) were recorded; the results are summarized in Table 1 . Sev-eral aspects of color pattern also were noted and are detailed under Results and Discus-sion. Specimens examined include: Colima, LSUMZ 7846; Durango, MSU 4434-36; Guanajuato, CAS 5848; Guerrero, LACM 130112; Hidalgo, MCZ 11432, UMMZ 99085; JaHsco, MSU 9801, 9803 (2 spec); Michoacan, FMNH 37116-22, 39058-61, 100098 (holotype of T vicinus), 126499-504, LACM 65252, MCZ 56019, 131014, UIMNH 23414, 23435, UMMZ 102510, 104699, 112537, 112541, 119409-12, 121546, UTA R-6050-52; Oaxaca, AMNH 97889, 103091, 103100, 107001, EAL 1797, LACM 130111-12, LSUMZ 7560, UF 11326-27; Queretaro, TCWC 53068; Sinaloa, CAS 24077, 24082, KU 40349, 78923, 83413, LACM 130113, MSU 567; Zacatecas, UMMZ 118433.