STUDIES ON THE ARACHNID ENTOSTKENl'lE. 229 



diifou reins^ one of the Yejovidae. In this species the laternl 

 crests which arise from the anterior cornua are better 

 developed than in PalamnasuSj and the homologue of the 

 solid lateral process of the latter is less solidified and rigid. 

 Moreover the anterior process from the neural arch appears 

 to be undeveloped (PI. 14, fig. 21). 



In Hadruroides charcasus, a member of the same 

 family as lurns, but with the sternum showing a mai-kedly 

 greater degree of antero-posterior compression, the " body " 

 of the entosternite is relatively much shorter tlian in the last- 

 named genus, thougli in other respects the entosternites of 

 the two are very similar. 



The process of reduction in tlie size of the entostei-nite by 

 longitudinal compression is carried to an extreme in the 

 Bothriurid[e (olim Telegonida;), where the steinum is 

 reduced to a transversely linear sclerite wedged in between 

 the genital operculum and the coxse of the appendages of 

 the fourth pair (= second walking leg). In Bothriurus 

 bonariensis (see PI. 14, fig. 22) the portion of the body of 

 the entosternite which forms the roof of the neural canal 

 is reduced to a narrow transverse bar. This modification 

 seems to have been accompanied by the disappearance of 

 the anterior pair of dorso-ventral muscles; those of the second 

 pair pass up to the aortic foramen without fusing with the 

 diaphragm. As in the genera of Vejovidas examined, 

 the subneural process is apparently absent in the Both- 

 riuridas. The structure of the entosternite in this family 

 bears out the view I have elsewhere expressed that these 

 scorpions are a specialised offshoot of the VejovidjB. 



In the Buthida), which are characterised by a triangulai-ly 

 compressed sternum, the entosternite shows unmistakable 

 signs of lateral compression, the " body " being reduced to 

 a longitudinal bar, from the posterior extremity of which, 

 and rather between than behind those of the first pair, rise, 

 in juxtaposition, the dorso-ventral muscles of the second pair. 

 The lateral crests are well developed, as in the Vejovida?, and 

 the subneural arch is furnislied with a median process 



