598 



ARTHROPODA. 



the order in which there is a complete metamorphosis, the pupa 

 being inactive, and comprises the Ant-lions (Myrmeleontidcz), the 

 Aphis-lions (Hemerobiidce), the Scorpion-flies (Panorfiidce), and the 

 Sialidce. The first of these groups is doubtfully known by fossil 

 forms in the Tertiary rocks, but the three last have representatives 

 in the Jurassic rocks, and are also found more or less abundantly in 

 deposits of Tertiary age. 



Lastly, the group of the Trichoptera comprises the Caddis-flies 

 (Phryganeidce), in which the anterior wings are generally hairy, the 

 larvae are aquatic and usually reside in tubular cases formed of 



Fig. 448. — Petalia longialata, a fossil Dragon-fly from the Lithographic Slates (Jurassic) of 

 Solenhofen. (Copied from Scudder and Zittel.) 



small foreign bodies, and the pupae are inactive during the greater 

 part of their life. A few Mesozoic forms of the Caddis-flies are 

 known, and various Tertiary types have been recognised. The 

 principal palaeontological interest of the Caddis-flies arises, however, 

 from the fact that the tubular cases of the larvae, formed of small 

 fragments of stone or of minute shells cemented together, are capable 

 of preservation in the fossil state. Such cases have been found in 

 the Cretaceous rocks of Bohemia and in various Tertiary deposits, 

 and they sometimes occur in such numbers as to give rise to deposits 

 of considerable thickness. Of this nature is the so-called " Indusial 

 Limestone" of Auvergne, which covers considerable areas, and attains 

 a thickness of eight or ten feet. 



