Nvcras. 9" 



superciliaries ; (5) lower eyelid without transparent disc ; (6) no 

 denticulation in front of the ear-openin<i[ ; (8) cylindrical or feebly 

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

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

 head or body. 



The main principle* 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. hoJubi, and in N. tessellata (txniolata. Smith). In the latter species 

 the markings may vanish towards the posterior part of the body 

 and the streaks on the sides break up into spots, and, further, 

 rearrange themselves into cross-bars, as happens also in iV". intertexfa, 

 var. IwJuhi. The dorsal striation may disappear and lead to ocellated 

 forms (iV. iniertexta, typica). The most pronounced ocellar pattern, 

 accompanied by the loss of the longitudinal streaks, is exemplified l)y 

 N. cJelalandii, 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 iV. tessellata. where three dorsal 

 streaks are present on the nape and four on the body. 



There are two important points in which the striation in Sncras 

 differs from 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 — a primitive condition in accordance with Eimer's law. 



Synopsis of the Species. 

 I. No small scales between the supraoculars and the superciliaries, or one to 

 three exceptionally present ; head not or but little broader than deep ; 

 16 to 22 lamellar scales under the foixrth toe. 



Head 4 to 5 times in length to ventr ; foot as long as or a 

 little longer than head ; parietal foramen present ; 40 to 51 

 scales aci"Oss middle of body ; ventrals in 28 to ;?2 transverse 

 series ; transversely enlarged plates under the fore-arm. 



1. N. emini, Blgr., p. 10. 



* Cf. Ann. S. Afr. Mus. xiii, 1917, pis. vi and vii, where the principal j^atteins 

 of markings have been figured. 



f The head is measured to the posterior border of the ear-opening, the skull 

 being considerably longer than the pileus, thus accounting for Bedriaga's 

 statement that the ear-opening is situated further back than in Lacerta, "on 

 the side of the neck." 



