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Show 1881.] LIZARDS FROM ECUADOR. 229 Peters as Cercosaura {Pantodactylus) argulus. Although the number and arrangement of the prseanal scutes affords a conspicuous and important character in the family Cercosauridse, and in many cases a reliable one, sufficing, for instance, to distinguish several species of Leposoma ivom the original one of Spix, and from the new one recently described by Prof. Peters, allowance must be made for a certain amount of variation in this particular, more especially as corresponding variations in other characteristic portions of the scu-tellation are to be found in the Lizards of this and closely allied South-American groups. I have already noticed that the internasal plate is sometimes entire and sometimes bisected in Neusticurus ecpleopus, Cope, although this species was described by Prof. Cope as differing from N. bicari-natus, L., in having it entire (see 'Ann. N. H.' Oct. 1879, p. 295). I found also in N. bicarinatus an irregular additional prsefrontal plate associated with the cleft internasal. In the present series of specimens of Cercosaura {Pantodactylus) argulus, the internasal has a longitudinal cleft in a line with the suture of the fronto-nasals, and occasionally the above-mentioned supernumerary plate is present in exactly the same position as in Neusticus bicarinatus. The fronto-nasals are in that case reduced to smaller triangular and more lateral plates, quite separated from each other, instead of being large and extensively in contact. These two forms of arrangement of the nasal shields are associated with two distinct types of prseanal scu-tellation. One specimen with the additional prsefrontal has four narrow marginal prseanals; another with the normal nasal plates has only two large rounded marginal prseanals, like Cercosaura ocel-lata, while the others have the normal nasals and the four narrow marginal prseanals. As Prof. Peters had only a single specimen from Bogota, and those in the present collection from Ecuador show a range of variation within recognizable specific limits, I give the following supplementary description :- 3. CERCOSAURA (PANTODACTYLUS) ARGULUS, Peters, Abh. Ak. Berl. 1863, p. 184, pi. i. fig. 3. Internasal broad, single, or bisected in a line with the suture of the two good-sized fronto-nasals when these are extensively in contact ; sometimes an intermediate small prefrontal joining the frontal and the internasal. Frontal and fronto-parietals of the ordinary shape, interparietal large, flanked by two large parietals, and followed by a small occipital enclosed between two good-sized postoc-cipital plates. Nasal rather large, followed by a single large frenal. Supralabials six, none particularly elongate; infralabials five, the third very elongate. Two pairs of large postmentals in contact, the third smaller, separated by the group of large and small intervening gular scales. Two contiguous rows of larger plates to the chest, where a small collar is formed by a central and two lateral rounded plates. Some convex scales behind the occiput; scales of the back not very narrow, keeled, pointed, the keels being slightly produced; on the |