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Show 300 DR. II. GADOW ON EVOLUTION [Mar. 20. A Key, or general definition of the main groups of Mexican and North-American Cnemidophori. 4 supraoculars. Collar composed of large scales. Posterior surface of forearm covered with granules. U.S.A. into Northern Mexico. C. sexlineatus*, p. 302. 4 supraoculars. Collar composed of large scales. Forearm normally with scutes, or enlarged polygones Centred or gularis-group, p. 327. 4 supraoculars. Collar composed of small scales, especially the rows which form the posterior edge. Forearm posteriorly covered with granules North-Western or tessellatus-groupf, p. 367. 3 supraoculars. Collar composed of large scales. Forearm granular Southern or deppei-group, p. 308. For comparison I give a few data of the South-American forms of Cnemidophorus. The first 5, C. ocellifer to C. longicauda, are closely allied to each other, and are all from Southern South America, i. e. extratropical. They are distinguished by the very small number of femoral pores; the position of the nostril is in the first nasal, i. e. " anterior to the nasal suture," as in the Mexicans (in the other South Americans the nostril lies between the two nasal plates); wheu there are only 3 supraoculars, this is due to reduction of the anterior scute, instead of the posterior as in the Mexicans. In this respect, therefore, the mere number is no indication of relationship with the dep])ei-group; it is rather the reverse. W e observe the same differences in the shape of the collar, some of the tessellatus, others of the gularis type : with or without granules at the edge, and, e. g. C. leachi, with intermediate conditions. The humerus is covered either with many small rows, or a few large rows, followed by smaller rows. But all the South-American species agree with the tessellatus and deppei groups in the entirely granular covering of the posterior side of the forearm ; there being not one specimen known with scutes or even enlarged polygones. Concerning the colour-pattern there seems to be the same amplitude of variation from adult species with many sharply defined stripes to those in which the stripes fade away, or are dissolved into round spots, mostly also with field-spots, e. g. in C. lemniscatus ; lastly there are some which attain a monochrome condition. * Hereto possibly also C. hyperythrus, distinguished by the fusion of the two frontoparietals into one plate, p. 307. t Hereto possibly C. labialis, distinguished by the nasal opening being in contact with the second upper labial, p. 374. |