304 THE GEOLOGICAL RECORD [CH. 



had a very rich venation, and a size that would be considered 

 embarrassingly large in our modern world. Of the others, it may 

 be briefly said that a general survey shews that none of them can 

 be strictly placed in existing Orders, although the Orthoptera, 

 Plectoptera, Hemiptera and Odonata are almost certainly direct 

 descendants of forms similar to those found at Commentry. Most 

 of these insects, however, are placed in a separate Order, the 

 Palaeodictyoptera. From these, probably, side-branches broke 

 away, to give origin sooner or later to our existing Orders, while 

 the main mass died out. 



One of these side-branches, undoubtedly allied to the Palaeo- 

 dictyoptera, but just as undoubtedly allied to the Odonata of 

 to-day, was the Protodonata. Only some seven or eight species 

 are known, comprised in five genera and three families. But the 

 fossils are so well preserved, and have become such a centre of 

 interest, that we cannot underestimate their value towards a 

 correct view of the origin of the Odonata. Probably the best 

 known, and certainly the most wonderful, of all the Commentry 

 fossils is Meganeura monyi (fig. 156). the gigantic Dragonfly whose 

 restoration was first attempted by Brongniart. This magnificent 

 insect had a wing-expanse of 27 inches, thus far exceeding the 

 largest insects at present existing. It was undoubtedly a Dragonfly, 

 and would fall within the Order Odonata in its general form of 

 body and wing, and in the definition of its mouth-parts. But it 

 had four-jointed tarsi, and its wing-venation lacked those well- 

 known specializations characteristic of our present-day Odonata, 

 the pterostigma, nodus, and the quadrilateral or triangle. 

 Unfortunately, in Brongniart's time little was known of the true 

 significance of much of the details of venation as we view them 

 to-day. Handlirsch [67] has already corrected Brongniart's restora- 

 tion, as far as it fails to agree with the obvious design of the 

 preserved parts of the fossil wing. In fig. 156, I offer a further 

 restoration, including the probable design of the head and thorax, 

 based on a study of the allied Meganeurula selysi. This latter 

 species differs from Meganeura monyi, and agrees with our recent 

 Zygoptera, in possessing an unbranched radius in all four wings. 

 In M. monyi, the radius is unbranched in the hind-wing, but 

 in the fore-wing it has two large branches arising rather close 



