30 Alexander Petruukevitch, 



ments, the nth being represented by the operculum 



situated on the ventral surface Haptopoda 



+ first pair of legs pediform, not converted into a tac- 

 tile organ 14 



14. Four, 5 or 6 anterior abdominal tergites very narrow. 

 Dorsal surface of abdomen never divided into longitudinal 



fields Phalangiotarbi 



+ anterior abdominal tergites not conspicuously narrow. 

 Dorsal surface of abdomen divided into 3 or 5 longi- 

 tudinal fields Anthracomarti 



ORDER SCORPIONES 



Head completely fused with thorax. Abdomen twelve-jointed, 

 the last five somites forming the so called cauda or post-abdomen, 

 considerably narrower than the anterior seven. Telson with a poison 

 gland and sting. Chelicera three-jointed, chelate. Pedipalpi six- 

 jointed, chelate, powerful. Coxae of first and second pair of legs 

 with maxillary lobes. Abdominal tergites and sternites heavily 

 chitinized, connected laterally with each other by means af a soft 

 chitinous cuticle capable of considerable distension. Post-abdominal 

 segments without such pleural membranes, their sternites and ter- 

 gites completely fused in each segment. First sternite represented 

 by the genital opercula, second sternite by the basal joint of the comb. 

 Four pairs of stigmata leading to lungbooks in third to sixth sternites, 

 one pair to each sternite. Anus without operculum, at the end of the 

 twelfth abdominal segment, ventral to the poison gland. Two middle 

 eyes and two to five pairs of side eyes on cephalothorax, some recent 

 species completely blind. All recent scorpions are viviparous. 



The classification of recent scorpions is based entireh' on external 

 characters, the most important being : the shape of the sternum, the 

 structure of the comb, the position of spines on legs, the shape and 

 sculpture of the pedipalpi, etc. These characters should naturall}^ 

 be of the same importance for the classification of extinct scorpions. 

 Unfortunately it is not always possible to see all important characters 

 in the same Palaeozoic specimen and the knowledge of the group 

 remains therefore incomplete. There are several genera based upon 

 specimens which do not show the most important structures. The 

 position of such genera in the system is naturally not certcdn. Some 

 species, too, have been placed under genera which they most resemble, 

 i. e., owing to their general resemblance to the type species and not 

 on account of their generic characters which unfortunately have not 



