TERTIARY 93 



which is relatively early in the Tertiary period, the insects were 

 very much the same as those which prevail at present. 



Among the strata richest in insect remains are those of the 

 Green River of Wyoming, of Eocene date ; the famous Baltic 

 amber beds of Oligocene age, and the White River deposits of 

 Colorado ; the Miocene deposits of Florissant in Colorado, together 

 with those of Oeningen and Radaboj in Europe, and others. 



Collembola and Thysanura are well represented in Baltic Amber, 

 and excepting the Devonian remains previously referred to (p. 86) 

 they are unknown from pre-Tertiary deposits. The Collembola, 

 which have been revised by Handschin (1926), are representatives 

 of living genera pertaining both to the Arthropleona and 

 Symphypleona, while the Thysanura comprise Machilidse, 

 Lepismidae and a species of Campodea. 



The earliest undoubted Isoptera occurred in Eocene times and 

 became more abundant in the Oligocene and Miocene. The most 

 interesting forms are Mastotennes and Archotermopsis, which are 

 the most primitive known genera and are each rej^resented by a 

 single species at the present day. Specialised genera such as 

 Euterm.es and Termes were also living in Oligocene and Miocene 

 times. 



Lepidoptera are present in rocks of Eocene age onwards, but it 

 is practically certain that the order is of pre-Tertiary origin, and 

 it may be added that certain leaf mines of Upper Cretaceous age 

 are very possibly the work of their larvae. In Lower Oligocene 

 times a few butterflies and more numerous moths, referable to 

 living families, occurred in Baltic amber, and some further 

 remains of the order have been disclosed in the deposits of Miocene 

 date. Fossil Lepidoptera, however, give no information relative 

 to the evolution of the order, and we have still to seek for the 

 existence of Homoneura in geological times. According to 

 Professor Cockerell, the Micro^jterygidae are represented by a 

 specimen in Burmese amber (in the British Museum) and this 

 seems to be the only record. 



Coleoptera are extremely abundant in Tertiary rocks. A 

 number of modern genera were existing in Eocene times and more 

 than 430 species of beetles are known from Baltic amber, while 



