A M ERICA N PA LEO ZOIC INSECTS— HA NDLIRSCH. 



811 



Tlif liorizontal dhtrihatipv. of American r<iJeozoic in^eda — Continued. 



The foregoing^ table presents a series of noteworthy facts. We here 

 see that nearly all the orders occurring in America have likewise been 

 already recognized in analogous European beds; in like manner almost 

 all the families rich in forms have been identified in hoth parts of the 

 world. In such groups as first exist in single individuals, no sort of 

 conclusion as to their actual horizontal distribution can obviously be 

 di'awn, and it consequently follows that there is a striking agreement 

 in the Paleozoic fauna in both continents. Only one order (Blattoidea) 

 represented in the Paleozoic of America extends over into the Alesozoic, 

 with two families, while all other orders are replaced in the younger 

 formations by those more highly specialized. 



Moreover, from a percentile comparison of the number of forms 

 represented in the single orders in the various formations of the 

 Paleozoic, it follows that the Paleodictyoptera, which on morphological 

 grounds I consider the stem group of all winged insects, appear tirst 

 and decrease from the oldest beds to the younger, while the more 

 highly specialized orders (Prodouata, IMegasecoptera, Hadentomoidea, 



