178 ORIGIN OF LIFE IN AMERICA 



are situated in the southern States of North America. It is 

 suggested by Dr. Ortmann that the south-eastern centre of 

 the early forms of Cambarus originated from the more ancient 

 south-western one by a process of migration across the present 

 continent. May not these early forms have travelled eastward 

 from Mexico towards Cuba and Florida when the latter were 

 connected directly by land with Central America ? A species 

 of Cambarus still lives in the rivers of Cuba. 



Instead of mollusks or crayfish we may take almost any 

 group of North American invertebrates and readily discover 

 among them certain ancient forms, which are either confined 

 to small areas in the south-eastern States or have evidently 

 spread northward from a south-eastern centre. 



Scorpions, for instance, are universally acknowledged to be 

 a very ancient group. The genus Centrurus has its head- 

 quarters in the West Indies and Central America. Now 

 four species of Centrurus are known from Florida, viz., C. 

 gracilis, C. carolinianus, C. margaritatus and C. hentzi, the 

 latter being peculiar to Florida. The allied genus Tityus, 

 which is rather more southern in distribution than Centrurus, 

 has one endemic species in Florida, viz., T. floridanus.* 

 Altogether the southern part of Florida shows marked affini- 

 ties with the West Indies. There are also some species in 

 Florida such as Cupiennius sallei, Keys, not yet recorded from 

 the Antilles, which are known from Central America. Quite a 

 similar southern relationship has been noticed among many of 

 the Floridian Orthopteraf and the Coleopteraj One of 

 the most noteworthy genera of beetles recorded from Florida 

 is Rhopalomesites. It has spread northward as far as Dela- 

 ware, and reappears across the Atlantic in western and 

 southern Europe. 



As regards the dragon-flies and their allies (Neuroptera), a 

 few species are common to the West Indies and the northern 

 continent. Some of these may have flown, or have been con- 

 veyed by a storm, from one region to the other. Such a method 

 of colonisation, however, cannot Jiave been used'by Enallagma, 



* Banks, Nathan, " Arachnida of Florida," p. 142. 



t Eehn, J. A., and M. Hebard, " Orthoptera of Florida." 



| Schwarz, E. A., " Coleoptera of Florida." 



