AG AM A MUTABILIS. 
97 
I have tabulated 41 specimens. In 17 of them the skull is longer than the tibia, in 
12 it is shorter, and in the remaining 12 the two are equal. When the lizards from 
Algeria and Tunisia are separated out from the Egyptian specimens, it is found that 
9 out of the 17 Algerian and Tunisian lizards have the skull shorter than the tibia, 
4 have it longer, while in 4 these two parts are equal. On the other hand, in 
the Egyptian lizards, of which there are 24, 3 only have the skull shorter than 
the tibia, 13 have it longer, while in 8 it is equal. The Egyptian lizards have 
thus, as a rule, longer skulls than the members of the species in the extreme west of 
its distribution ; but at the same time individuals from exactly the same localities may 
have their tibise longer than the skulls and the reverse. Moreover, a young lizard 
from Mandara has its skull exceeding the length of its tibia to a greater extent than 
occurs in any adult ; but, on the other hand, a young specimen from Gizeh, only a little 
older than the foregoing example, has the skull and tibia practically equal. 
The following is a synopsis of these measurements : — 
Skull longer 
than tibia. 
Skull shorter 
than tibia. 
Skull and tibia 
equal. 
13 
4 
3 
9 
8 
4 
= 24 
= 17 
The length of the hind foot of this lizard is also subject to considerable individual 
variations. A male from the Algerian Sahara, with the head and body 80 millim. long, 
has a foot 22 millim., whereas another male from the same region, 12 millim. shorter, 
has its hind foot almost the same length as the former, viz. 2T7 millim. Similar 
variations occur in Egypt : e. g., a male with its head and body 73 millim. has its foot 
25 - 3 millim. in length, considerably in excess of the foot of a specimen measuring 
83 millim., in which it is only 23 millim. The fore limb also presents similar variations, 
which are brought out in the Table. The tail also varies greatly in its length 
irrespective of locality and sex ; but at the same time the tails of the western lizards 
tend to be longer than those of the eastern, and more especially longer than the tails 
of the lizards with the finer lepidosis — e. g., two males, one from Duirat and the other 
from Egypt, measuring respectively 63 millim. from snout to vent, have tails 115 
and 90 millim. long; that is, the eastern tail is 25 millim. shorter than the other, 
although there is no difference between the length of the bodies of the lizards ; and yet 
I cannot separate them specifically. 
In dealing with this North-African species I have taken the opportunity to compare 
some of the Tunisian and Algerian Sahara specimens and others from the littoral of 
the Nile delta with undoubted examples of A. ruderata, Olivier. I find it impossible 

