70 ARKIV FÖR ZOOLOGI. BAND 1. 



in correspondence witli tlie strong development of the maxil- 

 lary which in consequence of the position of the suture reaches 

 further forward. I am the more snre abont this as in a 

 qnite young V. niloticus (also from Cameroon) this sntnre 

 between maxillary and premaxillary is obliquely transversal, 

 almost as in V. salvator. 



Even the nasal process of the premaxillary is thicker in 

 V. niloticus than in V. salvator, the narrowest part being in 

 the former 2 V 2 mm., in the latter 1 mm. 



The general shape of the jaws of both lizards is also a 

 good deal different. The npper ontline of the mandible of 

 V. salvator is not mnch cnrved, but slopes rather slowly 

 downwards from the coronoid (conf. fig. 2) to the dental 

 which on the whole is almost parallel with the maxillary, 

 although it has a somewhat concave npper ontline. In V. 

 niloticus the slope of the coronoid is mnch steeper and the 

 upper ontline of the dental mnch more concave (conf. fig. 1). 

 Bnt this curve is not confined to the upper ontline alone; 

 the whole dentalc of the mandible is quite strongly cnrved 

 upwards anteriorly, so that both rami of the mandible form 

 together something like a narrow spoon. This shape of the 

 mandible is of course suitable for holding the shells in proper 

 position during the act of crushing them. In the young V. 

 niloticus, meanwhile, the teeth are still conical, the shape of 

 the lower jaw is less concave than in the adult and resem- 

 bles more that of V. salvator. In this stage the young V. 

 niloticus is probably wholly insectivorous and does not yet 

 prey on molluscs. In the adult V. niloticus the curving of 

 the mandible as described above makes the vertical height 

 of the anterior portion of the skull much greater than in 

 V. salvator, but the maxillary portion of the former is also 

 a good deal larger and more strongly convex on its outside. 

 The hind portion of the skull of V. niloticus is also in every 

 detail heavier and larger than the same of V. salvator, which 

 stånds in connection with the general stoutness of the former 

 and with its need of larger areas for the insertion of the, in 

 this species, more powerful muscles. Among features that 

 ought to be especially recorded is the difference in shape of 

 the parietal. In T", niloticus the posterior processes of the 

 parietal are much broader than in the other species and even 

 in the middle the parietal is prolonged posteriorly, so that 



