B R E V I O R A LIBRARY Museum of Comparative Zoology APR 5 1996 us ISSN 0006-9698 Cambridge, Mass. 18 April 1996 Number 505 A NEW GIANT PHENACOSAUR FROM ECUADOR Ernest E. Williams,' Gustavo Orces-V,^ Juan Carlos Matheus,^ and Robert Bleiweiss'' Abstract. A new giant Phenacosaurus from the eastern Andes (La Bonita-Santa Barbara Region) of Sucumbios Province of Ecuador is described. It, like P. inderenae Rueda and Hernandez, 1991, differs from all other species in reaching a maximum size of more than 100 mm and differs from inderenae in the smaller size of the largest class of heterogeneous scales (flat flank scales interspersed with smaller scales and granules). In the density of the largest class of scales, it resembles heterodermus and differs from nicefori Dunn, 1 944, and tetarii Barros, Williams, and Vilora, 1 996. From all the remaining species, it differs in having heterogeneous scales. INTRODUCTION The first giant phenacosaur, Phenacosaurus inderenae (>100 mm in snout-vent length [SVL]), was described by Rueda and Hemandez-Camacho (1988) from Gutierrez, in the southeast of the Department of Cundinamarca, Colombia, on the eastern slopes of the Cordillera Oriental of the Andes, syntopic or sympatric with P. heterodermus. Since that description, there has been an explosion of infor-mation concerning these lizards. New species belonging to several subgroups have been described: tetarii Barros, Williams, and Vi-loria, 1996, and euskalerriari Barros, Williams, and Viloria, 1996, both from the Venezuelan side of the Cerro de la Perija; neblininus ' Museum of Comparative Zoology, Harvard University, Cambridge, Massachu-setts 02138. ^ Departamento de Ciencias Biologicas, Escuela Politecnica Nacional, Apartado 17.01.2759, Quito, Ecuador. ' Apartado 17-17-742, Quito, Ecuador. ■* Department of Zoology, University of Wisconsin, Madison, Wisconsin 53706.