INSECTA. 59I 



The great majority of existing Insects are terrestrial in habit, and 

 almost all of those which are aquatic are inhabitants of fresh water. 

 For these reasons, the remains of Insects are by no means abund- 

 antly preserved in the fossil condition, and are chiefly found in 

 association with deposits of coal, or in lacustrine or fluviatile strata. 

 Moreover, the remains of this class of Arthropods are generally 

 found (except when preserved in amber) in a more or less frag- 

 mentary condition, and, under any circumstances, they cannot be 

 satisfactorily deciphered except by practised workers in the depart- 

 ment of Entomology. Between two and three thousand species of 

 fossil Insects have been already described, but for the reasons just 

 stated, it would be impossible here to deal with these in even a very 

 general manner. The student desirous of acquiring a detailed know- 

 ledge of the fossil Insects must have recourse to special works on 

 the subject, and, especially, to the admirable treatises published by 

 Mr Scudder (see ' Literature of Insecta '). All that can be at- 

 tempted here is to give a brief outline of the general geological 

 distribution of the class, and of the leading characters and range in 

 time of the great orders of Insecta. 



As regards the general geological distribution of the Insecta, the 

 oldest known insect is the Palceoblattina Douvillei, recently described 

 by Brongniart from rocks belonging to the inferior portion of the 

 Silurian (Upper Silurian) rocks of France. With the exception of 

 this ancient type, the earliest remains of Insects are found in the 

 Upper Devonian rocks of North America. " It is, however, only 

 when we reach the productive Coal-measures that we arrive at 

 insect-faunas of considerable extent, such as those especially of 

 Commentry in France and of Mazon Creek in Illinois. Other con- 

 siderable deposits are found in the Coal-fields of the Saarbriick and 

 Wettin basins of Germany, the Belgian and British Coal-fields, and 

 in America the Coal-basins of Nova Scotia and Pennsylvania. The 

 Permian offers comparatively few species, but some of these are of 

 particular interest (e.g., Eugereoii), and the Trias is almost wanting 

 in fossil insects, except in the South Park of Colorado, where about 

 twenty species have recently been obtained, affording transitional 

 forms among the Cockroaches. Later Mesozoic deposits have 

 yielded nothing in America, but much in England, where nearly all 

 the strata from the Lower Lias to the Wealden have been pro- 

 ductive. On the Continent of Europe prolific Liassic deposits have 

 been discovered at Dobbertin in Germany and Schambelen in Swit- 

 zerland, while the Oolitic beds of Solenhofen are world-renowned. 

 Scanty returns have come from the Cretaceous, but the early Ter- 

 tiaries have yielded an abundant harvest in the amber deposits of 

 the Baltic shore, the marls of Aix, and in America at Florissant and 

 Green River, while the Middle Tertiaries of Oeningen, Radoboj, 



