282 



DR. H. GADOW ON EVOLUTION 



[Mar. 20, 



This question must be left in abeyance. As a rule, however, the 

 largei- species seem to have more numerous scales upon the thighs 

 and elewhere than their nearest smaller relations. This may be 

 in the nature of things ; it is quite possible that these many- jointed 

 armourings cease to fulfil theii- purpose when the individual com- 

 ponents pass beyond a certain size. 



The presence or absence of a separate frenocular plate, so often 

 I'elied upon in systematic works, is quite unreliable. Its absence 

 is due eqvially often to suppression as it is to fusion with some 

 neighboui-ing plate. 



Text-fiir. 63. 



Lepidosis of the under surface of the foreann. 



A=C. mexicanns, Balsas No. 3. Right forearm. Several rows of enlarged 



polygones down to wrist. 

 15= f. inexicanus, Balsas No. 2. Right forearm. 

 C = C'. mexicanus, Cuernavaca No. 8. Left forearm. Large scutes. 

 D=C'. mexlcanus, Cuernavaca No. 10. Left forearm. Large scutes. 



It seems reasonable to assume that 4 supraoculars represent 

 the more primitive condition, whence, by reduction of either the 

 anterior or the posteiior scute, the number is reduced to 3. In 

 most of the text-figs. 61-83 these features are clearly visible. 



The comjjositiou of the collar and the pi'otection of the posterior 

 side of the forearm are difiicult to describe in a few words. To 

 avoid the drawback of vague terms, the reader is referred to a 

 series of illustrations which are intended to standardise the 

 phraseology employed in this paper (text-figs. 62, 63, 64, 65). 



Some systematists have laid stress upon othei- characters. 

 Peters, for instance, found that the first upper lal)ial was denti- 

 culated in C. deppei ; this is best seen on the inside, but it is by 

 no means always the case in that species, while it occui-s also, 

 occasionally, in C immutabilis, in C. communis fi-om Cozumel 

 Island, and perhaps in others. 



Unpracticable were also the, at first sight, great differences 

 whether the keel of the tail-scales runs parallel, subparallel, or 



