CRUSTACEA OF ALABAMA. 49 



terminally a very long, curved claw and a short spine. In the female the second anten- 

 nse are smaller and less powerfully armed. The inner branches of the swimming feet 

 are reduced, the terminal segment of the outer branch in the feet of the third pair bears 

 two spines externally, one long and one short spine apically, and five setae within. The 

 inner ramus of the fourth feet is reduced to a process bearing two long setae. The fifth 

 feet are minute. The caudal stylets are armed with three terminal setae and one outer 

 lateral one not far from the end. The fact that Dana failed to distinguish the sexes 

 makes it difficult to satisfactorily determine whether our species is new, especially from 

 rather meagre observations. 



CONCLUDING REMARKS. 



The study of the limited number of species above quoted seems to justify us in 

 assuming that the differences between the Entomostracean faunas of North America and 

 Europe are to be accounted for not, as would be expected, by variations due to discord- 

 ant evolution since the glacial period, but by the interpolation of species belonging to a 

 South American fauna, which is gradually blending with the circumpolar fauna. If this 

 be so, the theory that the Entomostraca reached their development before the glacial pe- 

 riod and were simply caused to move southward and at its close to return, deserves con- 

 sideration, though it may be nearer the truth to imagine that at the close of the period 

 of active glaciation, the suddenly-created glacial lakes furnished just the arena necessa- 

 ry for the rapid evolution of this wonderful assemblage of closely allied animals which 

 at first were generally distributed over the northern temperate zone. 



