50 DISTRIBUTION OF SCORPIONS. [CH. I 



marks their northern limit. In America they do not, 

 according to Mr Pocock, get quite so far north as this. 

 Although the scorpions are an extremely ancient race, 

 beginning in the Silurian, and occurring there and in the 

 Carboniferous in the shape of forms which hardly differ 

 from existing species, the modern representatives show a 

 range which corresponds with that of existing continents. 

 The existing scorpions are nearer to the carboniferous 

 Anthracoscorpii in that the feet terminate in two claws 

 instead of in the single claw of the Silurian Palceopkonus, 

 which Thorell has relegated to another group, the Apoxy- 

 podes, reserving the name Dionychopodes for the others. 

 Mr Pocock deduces from a comparison of the slight differ- 

 ences in structure between the ancient and the modern 

 forms certain facts of structure which may be looked upon 

 as archaic ; though these seem to those accustomed to the 

 structure of other groups very minute it is evident that 

 we must be content with them owing to the already 

 mentioned homogeneity of the group. In the most ancient 

 scorpions the lateral eyes are behind the median eyes, 

 which are placed at the front edge of the thorax. We 

 should regard therefore those scorpions in which the eyes 

 approximated most to this primitive position as the oldest. 

 Another point is the pentagonal sternum which though 

 lost in many adults reappears invariably in the young. 

 Finally the existing Buthidse contain genera in which 

 there is a spur upon the fifth joint of the last two pairs of 

 limbs, a structural feature which gets its importance from 

 the fact that it has also been described in the Silurian 

 Palceophonus. Indeed it is the Buthidse which show to a 



