158 Mr. T. D. A. Cockerell on Fossil Arthropods 



exceed 200, and may reach 250, or even possibly 300. The 

 described species are distributed as follows: — 



Diptera. — 72 species, of which 31 are Tipulida}. 5 genera 



extinct, out of a total of 44 genera. 

 Ilymenoptera. — 51 species. 10 genera extinct, out of a 



total of 40 genera. At least 1 additional ant has 



been set aside for Mr. Doniathorpe to describe. There 



are no bees. 

 llomoptera. — 9 species. 4 genera extinct, out of a total of 



9 genera. 

 Odonata. — 4 species, of 4 genera, none extinct. The 



collection contains many more dragonflies, which will 



be described by Dr. Tillyard. 

 Orthoptera. — 3 species of Gryllidse, of 2 genera, none 



extinct. Other Orthoptera, some very fine, remain 



undescribed. 

 Heieroptera. — 3 species, placed under two generic names, 



probably involving 1 or more extinct genera, but these 



not named. Tiiere are various species awaiting 



description. 

 Nenroplera, — 2 species, of 2 living genera. 

 Lepidoptera. — 2 species, of 2 extinct genera. Other Lepi- 



doptera in the collection have been set aside for 



Mr. Durrant to describe. 

 Isoptera. — 2 species of the Australian genus Mastotermes. 

 Trichoptera. — 2 species of the living genus Derteodes. 

 Mecaptera. — 1 species of the living genus Panorpa. 

 Corrodeniia. — 1 species of the living genus Fsocus. 

 Thysanoplera. — 1 species of the living genus Aeolothrips. 

 Coleoptera. — 1 species of the living genus Pterostichus. 



Very many other beetles await description. 



The total number of extinct genera, as the records stand, is 

 21. It has seemed surprising that more were not found, 

 since there are so many extinct genera in the later rocks of 

 Florissant, Colorado. The discrepancy is no doubt largely 

 to be explained by the fact that the greatest amount of generic 

 differentiation occurs in those groups which depend on parti- 

 cular genera of plants, especially woody plants. These 

 groups — e. c/., Honioptera, Lepidoptera, plant-feeding Coleo- 

 ptera — have been neglected in the Gurnet Bay fauna, prefer- 

 ence being naturally given to those insects which could 

 readily be assigned to definite genera. The generic assign- 

 ment of beetle-elytra and fragmentary remains of Hemiptera 

 is hazardous, and doubly so when one is not well acquainted 



