86 PALEONTOLOGY 



narrow bases and correspondingly reduced anal area. The 

 venation is characterised by Rs with three or four branches ; 

 M with four branches ; Cug reduced and approximated to Cu^, 

 and the anal veins reduced to lA or with a vestige of 2A also. 



The Protodiptera are undoubtedly the most distinct of the 

 above supposed sub -orders, but so far no annectant forms have 

 been found between them and the true Diptera. 



It is probable that future discoveries may result in bringing 

 to light forms connecting the Paramecoptera {Belmontia) with 

 existing Protomecoptera, justifying the merging of the former 

 with the latter. Whether Parahehnofitia is really closely connected 

 with Behnontia seems doubtful. 



The Geological History of Insects 



The sequence of the appearance of insect remains in geological 

 times is displayed in the accompanying table (p. 101), and the chief 

 facts in the past history of these animals will be briefly discussed 

 in the light of recent discoveries. It may be pointed out that no 

 insect fossils have so far been found in any pre-Devonian rocks. 



Devonian. The presumed insect remains of this period are 

 extremely small and fragmentary, and have been found in flakes of 

 Rhynie Chert from the. Middle Old Red Sandstone of Scotland. 

 The most complete remains consist of portions of the head- 

 capsule, mouth-parts and antenntje of the species Rhyniella 

 prcecursor Hirst and Maulik, which is regarded by Tilly ard 

 (1928a) as being an early Collembolan. The other fossils consist 

 of mandibles only, and the species to which they have been 

 relegated, viz., Rhyniognatha hirsti Till., may possibly have been 

 a Thysanuran. If, as apj^ears very probable, Rhyniella is a 

 species of true Apterygota, it is remarkable that no evidence of 

 the existence of such insects has so far been revealed in inter- 

 vening rocks until the Oligocene period. 



Carboniferous. Remains of insect life are found in comparative 

 abundance during this period, and the earliest undoubted examples 

 of the class occur in the lower layers of the Upper Carboniferous 

 of North America. This early fauna consisted almost entirely 

 of Palseodictyoptera, Protorthoptera (including Protoblattoidea), 



