^O PSYCHE [April 



West Indies into Florida. Relative to the last I may be permitted to give a word 

 of caution. South American forms may reach Plorida by two lines of diffusion ; 

 one by way of the Antilles, the other by way of Panama, Yucatan, and Cuba, as 

 illustrated by Halisidota citripes. 



We will now take up each of these several gateways of natural dispersion and 

 discuss them separately as the northwestern, the southwestern, and the southeastern 

 sources of diffusion, after which we will consider another series of avenues taken 

 by such species as have been introduced into North America through the agency 

 of man. 



Diffusion from the Northwest. 

 i^See map. Boreal trendy F. F.) 



It is obviously impossible to discuss all the species, or even genera, that appear 

 to have come to us, or perhaps rarely gone from us, via this direction. I have, 

 therefore, selected the Coccinellidae, or lady-beetles, as an illustration, for the rea- 

 sons that the species are common, well known, and generally diffused over North, 

 and in some cases over South, America, and that the family is represented gener- 

 ally over the world, species of the genus Scymnus having been found in America, 

 Europe, New Zealand, Galapagos and Hawaiian islands, and also in the American 

 Tertiary deposits in Colorado and Wyoming. For illustrations I have as a rule 

 selected our most common species. Coccinella ^-notata occurs in Siberia, Alaska, 

 Hudson Bay, Greenland, Kansas, Utah, California, and Mexico. Cocciuella trifa- 

 sciata occurs in Lapland, Siberia, Oregon, and about Lake Superior. Hannonia 12- 

 macnlata occurs from Siberia to Hudson Bay and Lake Superior. Megilla jnacu- 

 lata, one of our most common species, occurs from Canada and Vancouver south 

 to Chile, with a larger variety of it occurring in Brazil. Eriopis connexa occurs 

 from Vancouver to the Straits of Magellan, and though confined to the west coast 

 in North America extends to the east coast in South America, and has been taken 

 on the Andes at from nine to ten thousand feet above the sea. The common 

 Hippodaniia parenthesis, a representative of H. amoe/ia in Siberia, occurs from 

 Oregon to Kansas and New Jersey. It is one of our most numerous and bene- 

 ficial species. CoccineUa g-notata, even more abundant and beneficial, occurs from 

 Canada to Guatemala. Cocchiella affinis occurs from the Lake Superior region 

 southward to Honduras, while C. sanguinea occurs all over North America and 

 from Alaska to Patagonia. 



Species coming from the eastern to the western hemisphere do not necessarily 

 occupy the same climatic areas in both. The following will suffice to illustrate this 



