354 NATURAL SCIENCE. May. 



surprising that such small links as we require have not yet been 

 found. 



The relationship between the fossil and recent Scorpions has 

 been summarised in the classification proposed some few years back 

 by Dr. Thorell. According to this system, these animals are divisible 

 into two great groups — the Apoxypodes, or those with pointed feet, 

 including the Silurian PalceopJionus, and the Dionychopodes for the 

 Carboniferous Anthracoscorpii and the existing Neoscorpii, all of 

 which have feet terminating in a couple of moveable claws. The 

 chief distinctive feature between the two last-named divisions is the 

 situation of the median eyes in the Anthracoscorpii close to the front 

 border of the carapace, and in front of the lateral eyes. This archaic 

 character, which is very noticeable in the Scorpion's relatives — 

 Thelyphomis, Phrynus, and Galeodes — has not been retained by any 

 existing genus of Scorpions ; but, in the absence of evidence to the 

 contrary, it seems justifiable to conclude that those recent forms in 

 which the median ocular tubercle is in the anterior half of the carapace, 

 approach the Anthracoscorpii more nearly than do those in which 

 this tubercle is placed in or behind the middle of this plate. Judged 

 by this test, the Scorpionidae constitute the most specialised group ; 

 for in some of the genera of this family the eyes have moved back 

 far past the middle of the carapace. In the luridae, Buthidae, 

 Chactidae, etc., on the contrary, the eyes are in the anterior half of 

 the cephalothoracic shield. 



Another test of specialisation seems to be furnished by the form 

 of the sternum of the cephalothorax. In most Scorpions this plate is 

 pentagonal ; but in the majority of the Buthidae it is reduced by lateral 

 compression to a small longitudinally triangular sclerite, and in the 

 Bothriuridae by antero-posterior compression to a transversely- 

 elongated plate. But that these two forms of the sternum are nothing 

 but specialisations of the pentagonal type is shown by the fact that in 

 the young of all Scorpions the pentagonal shape prevails. 



One more apparent criterion of primitiveness may be mentioned. 

 This is the presence in many of the Buthidae of a spur upon the fifth 

 segment of the last two pairs of limbs, this spur being seemingly 

 homologous with a spur which has been figured by Thorell upon the 

 corresponding segment of the legs in the Silurian Falcsophonus. More- 

 over, it is important to note that among the genera of Buthidae that 

 possess this spur are those that have the sternum of the primitive 

 pentagonal shape. 



In the Buthidae, then, and in no other group of Scorpions, we find 

 genera that still retain the three archaic characters that have been 

 mentioned, namely, the forward position of the median eyes, the 

 pentagonal sternum, and the so-called tibial spurs. We would 

 suggest, too, that the presence of a greater than the normal number 

 of lateral ocelli in some of the Buthidae may prove to be of interest in 

 this connection. The usual number of these organs is three on each 



