606 THE AMERICAN NATURALIST [Vol.L 



trurus, shows that their sternum retains throughout life 

 traces of its origin from a pentagonal prototype. Only 

 the triangular apex is comparatively small and more or 

 less hidden between the coxae, and the sides of the ster- 

 num are strongly convergent, not parallel. The sternum 

 in adults of various species of Buthinae of the Old World 

 shows also a small triangular apex hidden between the 



coxae, and in the absence of material I venture the predic- 

 tion that the embryos will be proved to possess a pentag- 

 onal sternum. 



Keeping this in view, let us now compare Centrums 

 infamatus with Eoscorpius typicus of the Pennsvlvanic 

 from Mason Creek, Illinois, a rather well-preserved Palae- 

 ozoic scorpion of approximately the same size. Fig. 4 



