Among the reptiles and amphibians which Hans Gadow collected in Mexico in 1908 was a series of ten iguanid lizards deposited in the collections of the British Museum (Natural History). Of these, one specimen was sent to the Museum of Comparative Zoology and was subsequently made the type of Ctenosaura (Enyaliosaurus) clarki by Bailey (1928). Until now, there has been no further report concerning the species. We found it locally abundant in the Tepalcatepec Valley in Michoacán, where observations were made during June and July, 1955; April, May, and August, 1956; and June, 1958. The data obtained from our preserved series, combined with the field observations, provide information concerning a species heretofore known solely as a name in checklists. Bailey (1928) cited Gadow's original locality as "Ovopeo, 1000 feet." So far as we know there is no such place name with this spelling in Michoacán. Two similar names of places exist - Opopeo and Oropeo. Opopeo, which lies at 9000 feet in pine forests south of Pátzcuaro, is out of the range of the species. Oropeo, however, at an elevation of about 1000 feet in the lower Tepalcatepec Valley about 8 miles south of La Huacana is, in all probability, the place where Gadow secured the specimen that later became the type.