ABT. 9 



SCORPIONS OF WESTERN UNITED STATES — EWING 



But four families of scorpions occur in the United States and 

 northern Mexico. These may be separated as follows : 



KEY TO THE FAMILIES OF SCOKFIONS OCCURRING IN WESTERN UNITED STATES AND NORTHERN 



MEXICO 



A*. Sternum subpentagonal, with sides almost parallel. 



B\ Membrane at base of last tarsal segment of most of the legs with a sin- 

 gle spur ; postabdomen frequently reduced Scorpionidae. 



B*. Membrane at base of last tarsal segment of most of the legs with two 

 spurs. 



C\ Only two ocelli on each lateral margin of carapace Chactidae. 



(Only one genus, Broteas, in United States and Mexico.) 



C*. With 3 to 5 ocelli on each lateral margin of carapace Vaejovidae. 



Sternum triangular, the sides being strongly convergent anteriorly ; mem- 

 brane at the base of last tarsal segment of most of the legs with two 

 unbranched spurs ; fixed arm of chelicerae without ventral tooth. 



Buthidae. 



'vesicle 



Supemumefanf C ' 



'' -teeth 



A' 



/fiddle rows 

 of LeetK 



SubatuUar 



/Sting 



spine 



-Tarsal tlavws 



Protarsus 



Pedal spurs 



pure 



Tarsus 



mar_gi.ri 

 of carapace 



Pectin al -teetk 



Fig. 1. — Detail drawings of parts of Centruroidhs vittatus Sat to illustratb 

 structures of taxonomic importance: a, finger of chelicera ; b, left half of 

 sternal region of male ; c, caudal segment of male ; d, antero-lateral section 



OF carapace; E, last two segments of LEG IV 



Family SCORPIONIDAE 



In this family the sternum is subpentagonal in shape, the sides 

 being almost parallel. The membrane at the base of the last tarsal 

 segment of most of the legs bears a simple spur. The postabdomen 

 is usually somewhat, or even decidedly, reduced. 



The family is well represented in Central America and the tropical 

 regions of the Old World but is poorly represented in the central part 

 of South America and in the United States. Dr. de Mello Campos 

 (1924) mentions only a single species as occurring in Brazil, and but 



