334 



PALAEOZOIC SYSTEM OF ROCKS. 



Fig. 420. 



Fig. 421. 



Figs. 420 and 421. 



-Devonian Trilobites: 420. Dalmania punctata, Europe, 

 frons, Europe. 



421. Phacops lati- 



Fig. 422.— Wing of Platephemera an- 

 tiqua, Devonian, America (.after 

 Dawson). 



Insects. — We have already seen (page 326) that a very few insects 

 (cockroaches and scorpions) have been found in the Upper Silurian. 



We treated these as anticipations. In the 

 Devonian, for the first time, they become 

 somewhat abundant ; and, as was to be 

 expected, are found in connection with 

 the abundant land vegetation of that time 

 (Fig. 422). 



The Devonian, and, indeed, all the 



Palaeozoic hexapod insects, belong to one 



family, which has been called by Scud- 



der Palaeodictyoptera (old netted-winged), 



a generalized type connecting the Neuropters and the Orthopters. A 



chirping organ is believed to have been found in some. If so, it implies 



also an organ of hearing in these early insects. 



Fishes. — The grand characteristic of the Devonian is the introduc- 

 tion here of a new dominant class — Fishes — and of a new department, 

 and that the highest, to which man himself belongs — the Vertebrates. 

 This is, indeed, a great step in the progress of life. It is necessary, 

 therefore, to treat these somewhat fully. 



Commencing far back in the Upper Silurian, few in number, small 

 in size, and of strange unfishlike forms, with the opening of the De- 

 vonian fishes greatly increased in size and number, until the waters 

 fairly swarmed with them. Never since have fishes apparently been 

 more abundant, of greater size, or better armed for offense, and espe- 

 cially for defense. And yet all the species, genera, and even families 

 then existent, are now extinct. Not only so, but tyj^ical fishes — Tele- 



