306 ARACHNIDA — SCORPIONIDEA chap. 



seo-ments 3-6 and 8 — and demonstrated that those of segment 

 5 persisted, though without external aperture, as coxal glands, 

 and those of segment 8 as the genital ducts. 



Classification. 



More than 350 species of scorpions have been described, 

 but many of these are " doubtful," and probably the number 

 of known forms may be put at about 300. These are divided 

 by Kraepelin ^ into six families and tifty-six genera. The best 

 indications of the family of a scorpion are to be found in the 

 shape of the sternum, the armature of the tarsi, and the number 

 of the lateral eyes, while assistance is also to be derived from the 

 shape of the stigmata and of the pectines, and from the absence 

 or presence of a spine beneath the aculeus. 



The six families are : Buthidae, Scorpionidae, Chaerilidae, 

 Chactidae, Vejovidae, and Bothriuridae. 



Fam. 1. Buthidae. — Sternum small and generally triangular. 

 Tibial spurs in the tliircl and fourth legs. Generalhj a spur 

 beneath the aculeus. Lateral eyes three to jive in number. 



There are two sub-families : Buthinae and Centkurinae. 



The Buthinae, which possess a tibial spur, comprise fourteen 

 genera, most of them Old "World forms. The principal genera 

 are Buthus, which contains about 25 species, and Archisomctrus 

 with 20 species. One genus only, Ananteris, is South American, 

 and it includes only a single species. The genus Uro'plectes, with 

 16 species, is almost entirely African. 



The Centrurinae, without tibial spur, are New World 

 .scorpions, though Isometrus euroiiaeus {maculatus) is cosmopolitan. 

 The principal genera are Tityus with 30 species. Centrums with 

 13, and Isometrus with 6. 



Fam. 2. Scorpionidae. — Sternum broad and pentagonal, unth 

 sides approximately 'parallel. No tibial spur, but a single pedal 

 sp)ur. Generally three lateral eyes. 



Nearly a hundred species of Scorpionidae have been described, 

 distributed among iifteen genera. The following sub-families are 

 recognised : Diplocentrinae, Urodacinae, Scorpioninae, Hemi- 

 scorpioninae, and Ischnurinae. 



1 Das Ticrrcich, 8. Lief., 1899. 



