Introduction. 



some unknown reason (perhaps scarcity of food or 

 dearth of water) develop a migratory instinct, and 

 wander in countless swarms for long distances : on 

 several occasions they have been noticed far out to sea. 

 Among British Dragonflies, Libclluhx qiiadriinaciilata 

 (the Four-spotted), has this trait ver}- well developed, 

 and many flights have been noticed. 



Geologists tell us that the Dragonflies are a very 

 ancient group of insects, and, possibly because their 

 outer covering is somewhat hard, their remains are 

 fairly numerous. In fact, representatives of the N^ciiro- 

 ptera are amongst the oldest of fossil insects yet known. 

 The earliest traces of insects were discovered near St. 

 John's, in New Brunswick, in the upper portion of the 

 Old Red Sandstone system, and consisted of a few 

 broken wings of Ncnroptcra allied to the Ephcnicridtc, but 

 perhaps having some features in common with the 

 Orthoptcray' The earliest fossil remains that can 

 with certaint}- be referred to the Dragonflies, ha\e been 

 found in the Lower Lias of the Jurassic s}'stem, this 

 formation in the West of England having provided a 

 great number of specimens. The Stonesfield Slate of 

 the Lower Oolite and the Purbeck beds of the Upper 

 ha\'e also been fertile sources of supph' in England. 

 But perhaps the formation best known for supplying 

 fossil Dragonflies in large numbers is the Solenhofen 

 Slate of Bavaria. This formation supplied the fine 

 specimen of Cordiilcgastcr dresdciisis, Charp. {^Eschua 

 charpcntieri, Hagen), which Charpentier has depicted 

 in his well-known text-book.t The Tertiary series 



* "Geological Antiquity of Insects," by H. Goss, pp. 6, 12, &c. 



f " Libellulinse EuropDece," by T. de Charpentier, pi. 48, tig. i, 1840. 



