THE CANADIAN ENTOMOLOGIST. 109 



These do not include the ones subsequently recognized as 

 undescribed, such for example as Cymiis daviculns Fall., which 

 turned out to be new and was .described by Horvath as discors; 

 Emblethis arenarius, which comparison with European material 

 showed to be different and which is now known as vicarius 

 Horvath; Pentatoma juniperma, which is restricted to the other 

 side of the Atlantic, ours being described as new under the name 

 of persimilis Horvath. 



Returning to the larger aspect of the question, a consideration 

 of the hemipterous forms common to the two continents discloses 

 the fact that in preponderating numbers these are phytophagous and 

 parasitic, the majority being Homoptera of families notoriously in- 

 jurious to vegetation, namely, the Jassidae and Aphididae. The 

 total number of species of this order found on both sides of the 

 Atlantic is in the neighborhood of 160 to 170, a very small 

 number as compared with the Coleoptera. 



How are we to account for this dispersal? There are two 

 chief means, the one natural, by migration of the living beings of 

 their own impulse, and the other artificial, through the agency of 

 man. A large proportion apparently belong in the first category. 

 The small remainder, (including therein the classic examples of 

 the unsavory bedbug and other obnoxious personal parasites)",,. 

 owe their distribution undoubtedly to the more or less involuntary 

 agency of man. To-day the constant importation of nursery stock, 

 is bringing with it a constant transfer to this continent of various 

 plant pests. Fortunately, the strict surveillance on plants brought 

 from abroad has thus far held in check the spread of these insects 

 to any great extent. On the other hand, sometimes the good 

 perish with the bad, and important predators are fumigated out 

 of existence together with their prey. 



An examination of the forms which evidently owe their dis- 

 tribution to natural agencies has shown that the great majority 

 belong to Palaearctic genera and are in the main Palaearctic 

 species of the most widespread character. Take for example 

 Gerris rufoscutellatus Latreille, which is without doubt the Hemip- 

 teron of widest actual distribution next to Nezara viridula. It 

 is known across Northern Europe through Siberia, thence to 

 British Columbia and Oregon, ranging East to the Northern 



