70 GEOLOGICAL MEMOIRS. 



also numerous species of Bugs, which are very similar to existing 

 species. 



Of the second great order of ametabolous Insects, the Gymno- 

 gnatha [Neuroptera, &c.], I have particularly to notice the i^6e/^^^^^ 

 and the Termites^ both which families have a high geological import- 

 ance. They commence early in the Jurassic period, and have continued 

 throughout the cretaceous and tertiary periods down to the present, 

 although now they no longer play the part they formerly did. The 

 Jurassic LihellulidcE are all large, beautiful animals, and are all 

 Mschnidce or Agrionidce ; true Libellulce occur for the first time in the 

 chalk. Near to the genus MscTina come Gomphus and a peculiar 

 genus Heterophlebia., observed as yet in the Jurassic rocks only. The 

 AgrionidcE, which are much scarcer than the MschnidcB, belong for 

 the most part to the group Lestes, characterized by many fine areolae 

 in the reticulations of the wings. A peculiar group, Sterope, also 

 occurs in the lias and is again found at (Eningen, but has since be- 

 come extinct. In the tertiary period there existed, besides the genus 

 Sierope, other members of the Agrionidce, particularly species of 

 \Lestes ; and species of Mschna very similar to existing forms were 

 present, and LibellulcE proper. These were so plentiful at (Eningen, 

 that their larvae were amongst the most common animals there. It 

 appears therefore that in this family the u^schnidce and Agrionidce 

 first occurred ; and of the latter the many-celled-winged [vielzelligen] 

 before the rest. Further, the genus Libellula, at present so rich in 

 species, first appeared in the Chalk period, and was developed in 

 numerous species in the succeeding tertiary epoch. Still more re- 

 markable, however, than the Libellulce are the fossil Termites, those 

 singular animals that are at present so abundant in the Tropics, con- 

 stituting one of the greatest land-plagues of hot countries. Like the 

 Ants they live in large communities, building themselves curious habi- 

 tations, and feeding on vegetable matter. The Termites (two spe- 

 cies) appear first in the Jurassic, and subsequently in the cretaceous 

 and tertiary beds. I am acquainted already with nine species, the 

 majority of which are remarkable for their size ; one species is larger 

 than any one of the existing species. The Termites are most nu- 

 merously found at Radoboj ; and I know of two species from (Enin- 

 gen and three from amber. Some of these tertiary Termites resemble 

 Brazilian species, but the majority exhibit peculiar, extinct forms. 

 Their size and their great abundance allow us to infer the existence 

 of a rich vegetation in the demolition of which they were necessarily 

 occupied. 



That the Orthoptera comprise the oldest known insects has been 

 already mentioned. It is important to observe that the BlattidcE first 

 appeared in the carboniferous epoch, and have continued through all 

 subsequent periods down to our own time, and indeed in very similar 

 forms. The same may be said also of the Acridii and the Locust cey 

 with which the Locust-type commences, continuing down to the pre- 

 sent. Most of the tertiary Locusts belong to the (Edipoda, but 

 there also occurs the genus Gryllacris, still living in India. 



II. Of the Metabola we first meet with the Flies. At present these 



