OF WASHINGTON, VOLUME XIII, 1911. 11 



In discussion of the first two papers on the regular program, 

 Dr. Dyar said: In the fauna of North America there are two 

 very distinct elements, one a descendant of the early circum- 

 polar fauna and not introduced and the second coming up 

 from the south. In the Noctuidse, the Agrotinse are domi- 

 nant in America, but also well represented in Europe. This 

 element of the fauna probably arose in pre-Glacial times and 

 then was driven southward. In the Lepidoptera the species 

 in temperate North America coming from the south are in the 

 minority. Arctia caja is almost the same in Europe and 

 North America, and the form on the Pacific coast is most like 

 the European form. In Asia there is a form like that in the 

 Rocky Mountains. Halisidota comes from the south and is 

 not in Europe. The ancestors of //. maciilata probably came 

 up the west coast into California from Mexico, giving rise to 

 another variety in the Canadian Rocky Mountains and from 

 this the Eastern typical maciilata. The Limacodidse are both 

 from the north and the south, but the latter dominant. 



Mr. Rohwer said that in the Sphecoidea there are many ex- 

 amples. In Trypoxvlon the frigidnm group is found in both 

 Europe and America and is a northern element, while the 

 rn foci net n m group found on both continents is apparently a 

 southern element. The excavation group found only in 

 America is a southern element, and comes as far north as 

 New York. 



Dr. Howard remarked that Professor Webster was discus- 

 sing a modern diffusion, while Messrs. Dyar and Rohwer were 

 discussing the ancient lines. It must be remembered that 

 insect diffusion depends to a large extent on food plants. The 

 diffusion in the United States has followed the life zones 

 and the insects have tended toward their normal zones. 

 Horticulturists trying to broaden the habitat of plants have 

 not been encouraged. Meromyza is one of a class of insects 

 carried in packing and so easily introduced. Insects intro- 

 duced into the United States from Europe spread to their nor- 

 mal life zone. 



Dr. Hopkins said that we have to consider two factors very 

 different one influencing insects introduced and one influ- 



