344 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1953 



well known to systematists. Such categories are established for deal- 

 ing with organisms in a very limited period of geological time, not 

 with the whole geological record of a group, with annectent forms 

 appearing at intervals. This is an elementary concept for vertebrate 

 paleontologists, most invertebrate paleontologists, and paleobotanists. 

 In other words, most paleontologists have come to identify these 

 higher categories by trends or tendencies in a group, recognizing that 

 some of its members might even lack the specific structures indicated 

 in most of them. Unfortunately, many students of fossil insects have 

 not followed such a concept and have erected taxonomic categories, 

 such as families and orders, on single fragmentary specimens. Ac- 

 cordingly, some extinct orders of insects have been established on 

 either very vague features or peculiar structures that might not oc- 

 cur in another species. Altogether, as a result of such practices, 44 

 extinct orders of insects have been established — almost twice as many 

 orders as are usually recognized as now existing. From an extended 

 study of most of the material on which these extinct orders have been 

 based, I am convinced that only 10 of them deserve ordinal status; 

 the other orders can be combined or merged in one way or another. 

 In the following discussion, I shall refer only to these 10 orders. 



The insect fauna of the Upper Carboniferous period was basically 

 primitive, for although some neopterous orders were present, they were 

 in the minority. This was the only period in the history of the insects, 

 so far as is known, when this was the case. The paleopterous orders, of 

 which there were five, included three main types. One of these types, 

 comprising mayfly-like insects, was a complex of three extinct orders — 

 the Palaeodictyoptera, Protephemerida, and Megasecoptera. Of these 

 the Palaeodictyoptera were the most generalized ; they had prothoracic 

 wing flaps and in general the Carboniferous species showed a lack of 

 specializations. Unfortunately, nothing at all is known of the im- 

 mature stages of this order. 



Table 1. — Oeological ranges of existing orders 



EARLIEST 

 NAME OF ORDER GEOLOGICAL RECORD 



1. Collembola (springtails) Devonian [?] 



2. Entotrophi (bristletails) Late Tertiary 



3. Thysanura (silverfish) Triassic 



4. Odonata (dragonflies) Early Permian 



5. Ephemerida (mayflies) Early Permian 



6. Perlaria (stoneflies) Late Permian 



7. Orthoptera (grasshoppers, crickets) Triassic 



8. Blattaria (roaches) Late Carboniferous 



9. Isoptera (termites) Early Tertiary 



10. Dermaptera (earwigs) Jurassic 



11. Embiaria (embiids) Early Tertiary 



12. Corrodentia (book lice) Early Permian 



