68 ARKIV FÖR ZOOLOGI. BAND 1. 



are perfectly whole except when more or less digested, and 

 the grasshoppers have not even a leg broken. It may be con- 

 cluded from this that the development of the powerful jaws 

 of this Varanus with its large molars is a special adaptation 

 to its habit of devonring large and hard-shelled molluscs. 



To find ont how far, and in which respect this adaptation 

 had affected the structnre of the skull of the West African 

 Varanus (fig. 1) I have made a comparison between such a 

 sknll and another of a more typical Varanus viz. V. salvator 

 (kept in the Upsala Museum). This comparison can be 

 carried out in the more satisfactory manner because, through 

 a fortunate coincidence, both skulls are of almost the same 

 length and both must have belonged to old and fullgrown 

 animals. The skull of Varanus salvator (fig. 2) measures 



Fig. 2. Side view of the skull of a Varanus salvator. 

 2 3 nat. size. 



from the anterior tip of the premaxillary to the occipital 

 condyle fully 134 mm. and in the skull of the West African 

 Varanus . niloticus (fig. 1) the same measurement is not quite 

 136 mm. The difference in length between both is accor- 

 dingly not quite two millimeters and such a slight difference 

 does not seem to prohibit a direct comparison of the measure- 

 ments of other dimensions. 



The most striking difference between the two skulls that 

 makes itself apparent at the first look is the great height 

 and stoutness of that of V. niloticus (fig. 1) compared with 

 which the skull of V. salvator (fig. 2) seems very low (and 

 therefore long) and slender. 



The difference in stoutness might perhaps most properly 

 be expressed by stating the weight of both skulls. The skull 

 of Varanus salvator weighs only 57 grams and 5 decigrams 

 and that of V. niloticus not less than 155 grams and 7 deci- 



