46 TERTIARY INSECTS OF NORTH AMERICA. 



by its describer among the true spiders, but named Arthrolycosa only from 

 its somewliat marked araneid features. The remaining two are con- 

 sidered by their describers as true araneides and seem to be the only true 

 precursors of this group known to us from the paleozoic rocks; the propor- 

 tion therefore of the Araneides to other Arachnides is reversed between 

 Paleozoic and Cenozoic times. 



In the present volume we are able to more than double the number of 

 Arachnides (apart from the amber inclosures) which are hitherto known 

 from Tertiary strata, and, as we shall see further on, hnd some interesting 

 points of comparison between the European and American spider fauna of 

 Tertiary times. (February, 1881.) 



Since the above was written the number of known Paleozoic Arach- 

 nides has greatly increased and a large proportion of theih have been placed 

 in a distinct order, Anthracomarti Karsch, with eight or ten genera. (Octo- 

 ber, 18H9.) 



In the classification of the remains of these animals, from the almost 

 complete absence of such characteristic parts as the details of the structure 

 of the ocelli and palpi, it has been impossible to do much more than to indi- 

 cate the probable affinities of the species to living types by means of the 

 general resemblances which the form of the cephalothorax and abdomen 

 and the relative length of the legs furnish. In a few instances these can 

 hardly fail to furnish us with sufficiently clear evidence, while in others the 

 reference is plainly open to a greater or less degree of doubt, which it is 

 hoped future material will eventually extinguish. 



Order J^CJ^TilNJ^ ISTitzsch. 



Acarina are by no means rare in Tertiary deposits, the group being 

 better represented than any other Arachnides excei)ting the true spiders, 

 and it is quite in keeping with this fact that the only arachnid yet discov- 

 ered in the American strata not belonging to the Araneides should fall in 

 this group. Yet the group is unrepresented even in Mesozoic strata, while 

 the scorpions and their allies, nearly unknown in Tertiary beds, are pro- 

 portionally abundant in earlier times. The amber of the Baltic is partic- 

 ularly rich in Acarina, thirtv-five species being recorded therefrom, while 

 apart from the Arant'idtis this group is almost if not (piite the only one rep- 

 resented in the stratified deposits of Europe; feebly represented, indeed, 



