172 INVERTEBRATE PALAEONTOLOGY 



True Malacostraca occur first in .the Carboniferous, 

 though certain problematical Isopods have been de- 

 scribed from the Devonian. The group was but feebly 

 represented in the Upper Palaeozoic. 



Arachnids of the Limulus-ty^o. are not uncommon in 

 the Coal Measures (where they are often beautifully 

 preserved in ironstone nodules), but Limulus itself is not 

 known before the Trias. Cyclus, Belinurus (PL xii. fig. 8) 

 and Prestwichia are well-known Carboniferous types, 

 the last bearing a remarkable general resemblance to 

 Trilobites. Eurypterids are familiar fossils of the Old 

 Red Sandstone, where their often enormous size and 

 grotesque form are clearly gerontic characters, prepara- 

 tory to their imminent extinction. Pterygotus, Slimonia 

 (PI. xii. fig. 9) and Stylonurus are among the most 

 familiar British genera. The last-named type sometimes 

 attained a length of nearly six feet. Eurypterus itself is 

 rare in the Old Red Sandstone, but occurs in the Coal 

 Measures and is known by one survivor in the Permian. 



Scorpions and Spiders occur in some variety in the 

 Coal Measures, where they are accompanied by Myrio- 

 pods. That group appeared first in the Lower Old Red 

 Sandstone of Scotland. The most prolific locality for 

 discovery of Carboniferous Arthropods in England is at 

 Sparth Bottoms, near Rochdale. 



The Insecta, which show such overwhelming pre- 

 ponderance in the recent fauna, are found first in the 

 Carboniferous. Great numbers of types occur there, but 

 almost all belong to extinct orders. In some respects 

 these early forms were synthetic, combining features now 

 distributed among distinct orders. Insect-wings (often 

 dangerously like " fern " pinnules) are not uncommon in 

 the shales of the British Coal Measures, but the most 

 noteworthy locality for Carboniferous Insecta is un- 

 doubtedly the district of Commentry, in France. 



