SUBPHYLUM III INSECT A 795 



Among the Orthopterous Insects of the British series of Carboniferous rocks are 

 a number of forms allied to cockroaches, and nodules of the same age contain wings of 

 Palaeodictyopterous and allied Insects, some of them showing colour bands (Brodiea). 

 At Comm entry (Allier), France, is found the richest deposit of Carboniferous Insects 

 in the world, and this fauna has been ably investigated by Charles Brongniart 

 (1893) and later writers. Very numerous fossil remains are known from different 

 Mesozoic and Cenozoic horizons. The Insects found in the English and German 

 Lias are for the most part small and insignificant, but there are known a moderate- 

 sized dragonfly, and also a few Coleoptera. Various remains occur also in the Stones- 

 field Slate, Purbeck, Wealden, Bagshot Beds (Upper Eocene), and Bembridge Beds 

 (Oligocene) of England. Insects are well represented in the Lithographic Stone 

 (Kimmeridgian) of Bavaria ; in freshwater Oligocene deposits of Aix in Provence, 

 and especially in Baltic amber of the same age from East Prussia ; in the Miocene 

 brown coal of Rott near Bonn ; in the Miocene lacustrine deposits of Oeningen, 

 Baden, on Lake Constance ; and in similar deposits of Florissant, Colorado, also 

 of Miocene age. Many Insects also come from the Miocene deposits of Radoboj 

 in Croatia, and from the Indusial limestone of Lower Miocene age from Offenbach. 

 There is considerable reason to supjjose tliat Insects were more numerous in species 

 during Tertiary times than they are at the present day. 



In the system here adopted the winged or wingless condition is made the basis 

 for dividing Insects into two classes, Pterygogenea and Apterygogenea. The former 

 of these comprises forty orders, thirteen of which are entirely extinct. The lowly 

 organised class of apterous Insects comprises four orders, three of which have Tertiary 

 rejjresentatives as well as Recent, and the remaining order is without known fossil 

 representatives. 



If the opinion of Lankester and Bcirner, that the primitive Insects have a special 

 affinity with the Isopoda, be accepted, the discovery of Oxyuropoda in the Devonian 

 of County Kilkenny, Ireland, becomes of particular interest (see ante, p. 757). In 

 the view of G. H. Carpenter, a more general relationship between Insects and 

 Crustacea seems probable, so that this Devonian Isopod genus and the lowly organised 

 Pterygote order of Palaeodictyoptera must be regarded as having each advanced along 

 difterent lines of specialisation from their common ancestors. The common stock 

 from Avliich both Crustacea and Insecta are descended must surely have been Arthro- 

 pods with undifteren tinted trunk-segments, yet on the whole, resembling primitive 

 Crustaceans in structure, and possibly not very remote from Trilobites. 



Class 1. PTERYGOGENEA Brauer. 



Insects normally winged in the adult, or secondarily wingless, with faceted eyes, and 

 abdomen usually with nine or ten distinct segments. 



t Order 1. PALAEODICTYOPTERA Goldenberg. 



Head moderately large, rounded, ivith simple antennae, mouth parts adapted for 

 biting, and well-developed jaws. Two pears of wings, subequal in size, of similar form 

 and frimitive venation, incapable of being folded backward over the abdomen ; sometimes 

 a rudimentary third pair present on the first thoracic segment. Abdomen consisting of 

 ten nearly homonomous segments which often exhibit pleural lobes. Terminal segment 

 often with much elongated cerci. Thoracic legs similar. 



In tliis order the wing structure is very primitive (Fig. 1531), corresponding 



t This sign is used throughout the following pages to indicate that the systematic group referred 

 to is extinct. 



