This is the most abundant and widespread species of _Cnemidophorus_ on the coastal lowlands of Michoacán, where it ranges from sea level to elevations of about 500 meters. In this area it inhabits dense arid scrub forest and semi-deciduous broad-leafed forest. Both of these habitats are continuous, or nearly so, along the lowlands and foothills of the Sierra de Coalcomán. This in itself may explain the abundance of _Cnemidophorus lineatissimus_ and the relative scarcity of _C. deppei_ and _C. communis_ in the coastal area, for _C. deppei_ and _C. communis_ usually inhabit more open arid scrub forest, as occurs in the Tepalcatepec Valley. Living in the dense scrub forest with _C. lineatissimus_ is _Ameiva undulata sinistra_. ~Cnemidophorus scalaris~ Cope _Cnemidophorus gularis scalaris_ Cope, Trans. Amer. Philos. Soc., 17:47, 1892.--Chihuahua, Chihuahua, México. _Cnemidophorus scalaris_, Zweifel, Bull. American Mus. Nat. Hist., 117:72, 1959. Araro (2); Jacona; Lago de Cuitzeo (42); Morelia; 21 km. N of Morelia (4). Zweifel (1959a:72) assigned the small species of _Cnemidophorus_ having a relatively low number of dorsal granules and inhabiting the southern part of the Mexican Plateau to _C. scalaris_, which he diagnosed as rarely exceeding 100 mm. in snout-vent length and always having an average of less than 100 dorsal granules at midbody and usually less than 90. Forty-two specimens from the south shore of Lago de Cuitzeo (UMMZ 119558) have 80-91 (85.8) dorsal granules. Four specimens from 21 kilometers north of Norelia (UIMNH 6952 and UMMZ 104743) have 89, 78, 92, and 84 granules; one from Morelia (UMMZ 104742) has 78; two from Araro (UMMZ 119522) have 80 and 87; one from Jacona (UIMNH 24703) has 88. Since no large adult males are present in the series from Michoacán, an adequate comparison of coloration between these and populations on the northern part of the Mexican Plateau cannot be made. _Cnemidophorus scalaris_ is a name applied to the lizards inhabiting the Mexican Plateau from Chihuahua south to Puebla by Zweifel (1959a:72). It is doubtful if all of the populations assigned to this subspecies belong there; possibly more than one species is involved, but the paucity of material prevents further analysis at this time. ~Heloderma horridum horridum~ (Wiegmann) _Trachyderma horridum_ Wiegmann, Isis von Oken, 22:421, 1829.--México. Type locality restricted to Huajintlán, Guerrero, México, by Smith and Taylor (1950b:193). _Heloderma horridum horridum_, Bogert and Martín del Campo, Bull. Amer. Mus. Nat. Hist., 109:20, April 16, 1956. Apatzingán; Coalcomán; La Placita; Oropeo; Parácuaro.