PERLIDAE 



407 



species from all parts of the world existing in collections probably 

 scarcely exceed two himdred. The insignificance of this number 

 is no doubt chiefly due to the fact that these unattractive Insects 

 are rarely captured by collectors, and are so fragile that unless 

 good care is taken of them, specimens soon go to destruction 

 after being dried. Perlidae are known to occur in most parts 

 of the world, so that the number of species really existing may 

 reach two or three thousand. They are known to anglers as 

 stone-flies and creepers and are a favourite bait for trout. 



The family in its character comes near to the Orthoptera, 

 especially to the more simple forms of Phasmidae, but the two 

 groups differ in the texture of the 

 front wings and in the structure 

 of the mouth-parts, as well as in 

 the different proportions of the 

 mesothorax and metathorax. Ac- 

 cording to Pictet, in the Australian 

 genus Uusthenia the trophi (Fig. 

 259) approach nearer to those of 

 the Orthoptera, so that it appears 

 possible that a more intimate con- 

 nexion will be found to exist as more j,^^_ 259. -A, Maxilla, B, labium 

 forms are discovered. Of the groups of Ensthenia s^ectaMlis. (After 



we include in Neuroptera, Perlidae ''^ ^ '' 



are in structure most allied to Sialidae, but the develo]pment in 



the two groups exhibits very important distinctions. Brauer 



treats the Perlidae as forming a distinct Order called Plecop- 



tera, a name applied to the family by Burmeister many years 



ago. 



Several species of Perlidae, considered to belong to existing 

 genera, have been found in amber. A fossil from the Eocene 

 deposits in the Isle of Wight and another from the Miocene of 

 Continental Europe are referred to the family. Brauer has 

 recently described^ some fossils from the Jurassic formation in 

 East Siberia as forming three genera, now extinct, of Perlidae. 



Brongniart informs us ^ that several fossils have been found 



exists. References to the scattered descriptions and notes will be found in the 

 Catalogue of British Neuroptera published by Entom. Soo. London, 1870. 



^ 31em. Ac. Fiterab. (7) xxxvi. No. 15, 1889. 



^ Inscctes fossiles, etc., p. 407, 1893. 



