300 DR. H. GADOW ON EVOLUTION [Mar. 20, 



A Key, or general definition of the main groups of Mexican 

 and North- American Cnemidojjhori . 



4 supraoculars. Collar composed of large scales. 

 Posterior surface of foi-earm covered with 

 granules. U.S.A. into ISToi-thei'n Mexico. 



C sexlineatus*, p. 302. 



4 supraoculars. Collar composed of large scales. 

 Forearm normally with scutes, or enlarged 

 polygones Central or gularis-groii2y, p. 327. 



4 supraoculars. Collar composed of small scales, 

 especially the rows which form the posterior 

 edge. Forearm posteriorly covered with 

 granules Korth-Western or tessellatios-g^^oujj'f, p. 367. 



3 supraoculars. Collar composed of large scales. 



Forearm granular 6'outhern or deppei-group, p. 308. 



For comparison I give a few data of the Sotdh- American forms 

 of Gnemidojjhorus. 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, t. e. " anterior to the nasal suture," as in the 

 Mexicans (in the other South Americans the nostril lies between 

 the two nasal plates) ; when 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 deppei-grou]) ; it is rather the 

 reverse. 



We observe tlie same differences in the shape of the collar, 

 some of the tesseUatus, 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 tesseUatus and depjyei 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. Jahialis, distinguished hj the nasal opening being in contact 

 with the second upper labial, p. 374. 



