DISTEIBUTIOlSr OP AEACHKIDA. 285 



Owing to the very limited nature of insect faunas in general, 

 and the circumstance that only a few localities have thus far 

 yielded insect remains in any abundance, it is impossible to draw 

 any positive conclusions respecting either the geographical dis- 

 tribution or the genealogy of the members of this class of animals. 

 It appears practically certain, however, that the metabolous types 

 were descended from the ametabolous, and that the larvae of the ear- 

 lier forms were all, or mostly all, aquatic in habit. The geological 

 and horizontal range of the majority of the species appears to have 

 been very limited, but it must be recollected that in most instances 

 the number of individuals found representing any one given species 

 is altogether too small to permit of any logical inference being 

 drawn from their occurrence. Thus, of the numerous species of 

 Paleozoic cockroaches, by far the greater number are represented 

 by single specimens, or by specimens coming from a single locality. 



ABACHNIDA AOTJ MTRIAPODA. 



The earliest arachnoid remains (scorpions) occur in the Upper 

 Silurian deposits of the island of Gothland, Sweden, and Lanark- 

 shire, Scotland, and in the Helderberg rocks of WaterviUe, New 

 York, from each of which regions a single specimen has been ob- 

 tained. The Swedish species, Patoophoneus nuncius, with which 

 the Scotch form appears to have been nearly related, ranks among 

 the largest of its class, measuring about three and a half inches 

 in length ; in its general characters it closely approximates the 

 modern scorpions, although, as has been pointed out by Professor 

 Liudstrom, the structure of the large and pointed thoracic limbs 

 more nearly approaches what is seen in the embryonic forms of 

 other Tracheata and in Campodea. The presence of stigmata and 

 the whole organisation of the body clearly demonstrate the ani- 

 mal to have been an air-breather and an inhabitant of dry land. 

 The American form, Proscorpius Osborni, is less clearly recognisable 

 than the European, and some doubt has been thrown upon its 

 arachnoid nature, which is maintained by both Whitfield and Tho- 

 rell. Excepting these two or three earliest precursors of the Scor- 

 pionids3, whose presence would naturally seem to indicate a rich 

 insect fauna for the period, no traces of arachnoid remains are known 

 antedating the Carboniferous deposits, where, however, several well- 

 marked genera, singularly close in their relationship to modern 



