604 THE AMERICAN NATURALIST [Vol.L 



preserved fossils there remain then only the Silurian 

 Pahvoplionida' and the carboniferous Eoscorpionidae hav- 

 ing a sternum and arrangement of coxae similar to that 

 in recent scorpions. But the Silurian scorpions pos- 

 sessed other characters of their own and have either dis- 

 appeared completely or perhaps have changed gradually 

 into carboniferous forms. In the absence of Mesozoic 

 fossils any attempt to trace relationships between recent 

 and Palaeozoic scorpions can be only conjectural. Thus 

 in my "Monograph of Palaeozoic Arachnida" I arrived 

 at the conclusion (p. 26) that " the family Eoscorpion- 

 idae shows many relations to the recent Scorpionidae and 

 Vejovidae and represents probably two or three families 

 thrown together for lack of distinctive characters. " In 

 formulating this opinion I was guided chiefly by the shape 

 of the sternum, in several cases remarkably well pre- 

 served. Since that time I have made an observation, in- 

 significant in itself, but one which affords an insight into 

 the past history of recent scorpions possessing a trian- 

 gular sternum and suggests a closer relationship between 

 the Eoscorpionidae and the Centrurinae than between the 

 former and the Vejovidae. This observation was made 

 by pure chance. While studying the problem of seg- 

 mentation in Arthropods, I was examining a frontal sec- 

 tion through a recently born Centrums insulanus from 

 Jamaica (Fig. 2). To my amazement the sternum proved 

 to be beautifully pentagonal. An error of identification 

 was excluded. I myself collected the material and pre- 

 served the adult females with the young carried on their 

 back. Yet if objection should be raised, a final proof is 

 offered by the fact that late embryos, too, have a pentag- 

 onal sternum and such embryos are easily obtainable 

 from adult, gravid females. (Scorpions are without ex- 

 ception viviparous.) The young of Centrums infamatus 

 also have a pentagonal sternum, as have probably the 

 young of all other species of the genus Centrums. It is 

 strange that no one has noticed this before, since there 

 must be dozens of specimens in every museum. I find 



