Annals of the Transvaal Museum. 
121 
Karas Mountains and with P. punctatus , at Quibis. Now P. punctatus , 
P. jturcelli, and P. mariquensis are three closely related species, but no 
two of these were ever taken together. P. punctatus was found hiding 
under stones in the daytime in somewhat broken country : P. purcelli 
was invariably found in crevices of rocks at a fairly high elevation in 
the Great Karas Mountains : P. mariquensis of which only two 
specimens were taken was found at the foot of the eastern slopes of the 
same mountains in sandy soil. 
Two species of Agama were found, rather closely related species — 
A. atra and A. aculeata — , and in this connection again it was noticed 
that A. aculeata was in the Karas District invariably taken in sandy parts, 
whereas A. atra preferred the rocky parts of the mountains.* 
The two species of Zonuridae taken were found under precisely the 
same conditions as far as could be judged but not in precisely the same 
localities. 
Among the five species of Mcibuia which were taken it was noticed 
that the two which are most closely related, namely M. trivittata and 
M. occidentalism did not occur together : the former was found on rocky 
ground, in one case at the height of 6000 feet, the latter in the sandy 
river bed on the western side of the Great Karas Mountains. M. sulcata , 
not closely related to either of these two was found under various 
environmental conditions, often occupying the same locality as 
M. occidentals on the one hand, and as M. trivittata on the other hand. 
Again the three species M. sulcata ; M. varia and M: trivittata were 
found to occur together : but no two of these three species can be said to be 
closely related : M. sulcata and M. varia belong to the same group of the 
genus, but neither is so closely related to each other as either one is to 
M. striata , a species which was not taken on this expedition. 
We may conclude by saying that we have not found any instance of 
two closely allied species occupying precisely the same environment in 
the same locality.! The facts seem to us to point to the supposition that 
the formation of closely allied species is only possible when the diverging 
stocks can in some way be separated from each other (so as to prevent 
interbreeding), this isolation being frequently brought about in all 
probability by differences in habits. 
We do not wish to suggest however that all species are formed in 
this way though such may conceivably be the case : so far as one may 
judge from distribution data it seems possible that some species may have 
arisen without the aid of topographical or even habitudinal isolation. 
'* la August of this year I took a specimen of Agama atra and A. distanti together in 
the vicinity of Pretoria : both were found hiding under the same stone, and were probably 
hibernating. This is however the only case I have noticed, after numerous observations, of 
these two lizards occurring side by side. Further the habits of the two species are different. 
Thus A. distant i is usually found in the open veld, in flat country free of rocks : they live 
largely on termites into whose nests they frequently burrow : they are partly arboreal. 
A. atra on the other hand is found in the rocky hills : this species never, as far as I know, 
makes burrows but lives among the rocks, into the crevices of which it retires for conceal- 
ment. The third species of Agama in the Transvaal, namely A. atricollis , is probably 
exclusively arboreal. — P. A. M. 
f A partial exception" to this rule was furnished by Pacliydactylus bibroni var, 
laeviyatus which was found together with P. bibroni var. ty pious (but see page 129). 
