A Revision of the Lizard* <>f I In' <!>'imy Nucrcts, Gray. 197 



deuticulatiou in front of the ear-opening ; (8) cylindrical or feebly 

 compressed digits with smooth lamellae interiorly ; (10) the ideal 

 type of primitive markings in some forms, no vivid colours on the 

 head and body. 



The niain principles of the evolution of markings, as held by me, 

 are well supported by a study of the genus Nucras, which embraces 

 striated, ocellated, and barred forms. The most primitive pattern, 

 with 11 light longitudinal streaks, at least anteriorly, occurs in 

 N. intertexta, var. holubi, and in N. tessellata (taeniolata, Smith). In 

 the latter species the markings may vanish towards the posterior part 

 of the body, and the streaks 011 the sides break up into spots and, 

 further, rearrange themselves into cross-bars, as happens also in 

 N. intertexta, var. liolubi. The dorsal striation may disappear and 

 lead to ocellated forms (N. intertexta, typica). The most pronounced 

 ocellar pattern, accompanied by the loss of the longitudinal streaks, 

 is exemplified by N. delalandii, in which, further, the ocelli may 

 disappear, to be replaced by black cross-bars. As a rule the white 

 longitudinal streaks are more numerous on the nape than on the 

 body, but I find one individual exception in a typical N. tessellata, 

 which shows three dorsal streaks on the nape and four on the body. 



There are two important points in which the striation in Nucras 

 differs fi'om that in Lacerta : (a) The outer light dorsal streak, 

 instead of starting from the superciliary edge, originates on the 

 border of the frontal shield and then follows the supraorbital border 

 and the parietal shield ; (b) the vertebral streak, instead of ending on 

 the base of the tail, may be continued a considerable distance along 

 that organ ; evidently a- primitive condition in accordance with Eimer's 

 law. 



The distinction of species in this genus has always been a matter 

 of difficulty, all the greater for the small number of specimens which 

 most authors have had at their disposal. I have been so fortunate as to 

 be able to compare large series, preserved partly in the South African 

 Museum, partly in the British Museum. Not long ago* I attempted 

 a rearrangement into varieties from the South African material 

 entrusted to me by my friend Dr. L. Peringuey, but I have since 

 made a more profound study of the subject, resulting in the present 

 monograph, in which detailed descriptions are given of the species 

 and varieties. So much doubt still exists as to the value of certain 

 characters of lepidosis and coloration, that the minute analysis of 

 individual variations, as presented in this paper, will prove useful to 



* Ann. S. Afr. Mus. v., 1910, p. 473. 



