FALL AND COCKERELL. 



151 



erally, they are totally absent. On the western slope they go further 

 north, and one species just enters Wyoming; but there are none at 

 all in Wyoming, with this exception, and none in Montana. This 

 alone would explain the northward limitations to the distribution of 

 the numerous species of Coleoptera which are attached to the oak, 

 and various similar cases could be cited. It appears probable that 

 the oaks were driven south during the glacial period, and owing to 

 the uusuitability of their seed for being carried great distances, have 

 been unable to recover their lost ground. Under these circumstan- 

 ces, the ample powers of flight of certain of the oak feeding beetles 

 are of no service for promoting migration northward of the slowly 

 moving line of oaks. 



The following figures will serve to illustrate the diflerence between 

 the Colorado and New Mexico lists : 



Genera Species 



Colo. Botli. N. M. Colo. Both. N. M. 



Cicindelidffi _ 3. — 17. 25. 13. 



Carabidae 7. 42. 15. 159. 143. 72. 



Dytiscidffi 2. 10. 5. 40. 20. 19. 



Gyrinidge _ 2. — 7. 2. 1. 



Hydrophilidse 4. 10. 2. 18. 15. 14 



Silpbidse 4. 



25. 15. 2. 



Endomycbidfe — 3. 1. 3. 



Cerambycidse » 14. 34. 16. 55. 59. 52. 



It will be noted that New Mexico shows a greater proportion of 

 non-Colorado genera than species; or in other words, the species 

 found in New Mexico but not in Colorado are more likely to be of 

 non-Colorado genera than in the reverse case. This is explained by 

 the fact that the desert fauna in nearly all groups is rich in peculiar 

 genera, but these are represented so far up as New Mexico by com- 

 paratively few species. On the other hand, the boreal fiiuna, so 

 strongly developed in Colorado, is largely characterized by the 

 abundance of species of circumpolar genera. 



In Colorado the eastern plains region has been little searched for 

 beetles, and the corresponding region of New Mexico is also poorly 

 known. There is no doubt that the plains will furnish many species 

 additional to the lists, and most of these will doubtless be common 

 to both. The following are chiA-acteristic eastern species which are 

 known to reach New Mexico, but have not yet been found in Colorado- 



■*• One species is to be added to the Colorado fauna: Liopus dnereus Lee, Boul- 

 der (C). 



TBANS. AM. ENT. SOC. X.XXIII. MAY. 190/. 



