ANATOMY AND GENERIC CHARACTERS OF SCORPIONS. 375 



sinuses from drawing upon the blood which has already entered the lateral pericardio- 

 pulmonary veins. 



It is not at all improbable that the movements of the body-wall (terga and sterna) in 

 Scorpio and of the plastron (prosomatic entochrondrite) in Limulus, and, perhaps, also 

 in Scorpio, exert a considerable influence upon the flow of the blood. 



b. Generic and Subgeneric Characters of Scorpions. 

 The numerous species of Scorpions which occur in all parts of the world, excepting 

 the Arctic and Antarctic regions, and as far back in time as the Upper Silurian strata, 

 present a most marvellous uniformity of structure, so that the attempt to divide them 

 into families, genera, and subgenera has been a matter of great difficulty, and has led to 

 very perplexing and contradictory results in the hands of successive systematists. The 

 late Professor Peters appears to me to have indicated the most important divisions 

 which may be instituted among Scorpions on structural grounds. Dr. Thorell has 

 carried the formation of genera and subgenera too far, whilst the older system of Koch 

 is entirely artificial and worthless. No writer on Scorpions has given consistently a 

 clear statement or (what is more to be desired) good figures of the really important 

 structural features of the genera, subgenera, and species proposed or recognized by him ; 

 and it is with the object of pointing out what are the important points in which 

 Scorpions may vary that the present remarks are published. It is impossible to deal 

 with the genera of Ehrenberg and Leach. Starting with Koch, we find that he bases 

 his system on the number and disposition of the lateral eyes, as follows : — 



Scorpius O 



o 

 o 

 Buthus o 



O 



Atreus o 



o 



Brotheas „ 



Uo 



Telegonus O 



o 



Sisyphus cP 



o 



O 

 O 



Tityus o° 



o 

 o 



Androctonus ° ° 



vol. xi. — part x. No. 9. — May, 1885. 3 k 



