240 



PSYCHE. 



[August — December 1SS9. 



broad territory in the high northern lat- 

 itudes extending its range more or less 

 over the north of both hemispheres. 

 With the southern advance of the polar 

 ice-sheet this insect was driven far to the 

 south where the oceans and meridional 

 mountain ranges divided the original 

 form into at least three distinct families, 

 which, isolated from each other, and 

 under the influence of different environ- 

 ments, have been modified and be- 

 come fixed into the species as we now 

 find them. It would but poorly satisfy 

 the conditions of the case to suppose that 

 either foi'm, as at present distinguished, 

 has, after being introduced into the other 

 faunal regions, become modified to the 

 extent we find here. 



Therefore we doubtless have here three 

 . species of equal value and of the same 

 age, although not equally difterentiated 

 from one another. The similarity of the 

 climatic conditions surrounding the 

 European and Californian families 

 would naturally produce, as we find to 

 be the case, species more closely related 

 to each other than to the eastern Ameri- 

 can familv, surrounded as it was by 

 greater climatic variations and occupy- 

 ing probably a much larger area. This 

 view of the origin of these little green 

 pediopsids is in full accord with the 

 views of Mr. A. R. Grote. in regard to 

 the origin of the North American lep- 

 idopterous fauna, expressed in v. i of 

 the Bulletin of the Btiffalo society of 

 • natural sciences^ p. 200 and more fully 

 developed in 1S84 in v. iS of the Cana- 

 diatt entomologist. 



Some portions of the North American 



homopterous fauua very closely parallel 

 the corresponding European faunas but 

 I apprehend that but few species — such 

 as have been recently introduced, and 

 possibly a few others — will prove to be 

 actually identical with the Eiu'opean 

 forms. These many allied species, sug- 

 gesting so strongly a common origin, 

 belong to distinctively northern groups 

 that show as marked a parallelism in 

 genera as in species, and seem to be de- 

 cendants of a tertiary fauna common to 

 the northern parts of both hemispheres, 

 which in adjusting themselves to the 

 conditions imposed on them by glacial 

 action have been modified, some more, 

 some less, but few so little that they can 

 now be declared identical. A compari- 

 son of the European and American lists 

 of J-assidae will show a very large per- 

 centage of northern European genera 

 represented in boreal America. A few 

 peculiar groups of course appear, but 

 when our western hemiptera are better 

 known this general statement will, I 

 am convinced, find strong additional 

 verification. 



Of the species of hemiptera common 

 to both sides of the Atlantic some appear 

 to have undergone no change, such are 

 Cy7nus claviculus. Scolopostethus afi- 

 nis., Eeptopterna dolobrata., Opsioco- 

 etus personatus., Cicadula 6-notatus 

 etc. Others while practically identical, 

 exhibit modifications of structure or 

 marking, or tend to pi'oduce varieties 

 not strictly paralleled in the European 

 facies of the species, e. g. Hebrus pus- 

 illus^ Philaenus spumarius., Athysa- 

 nus striola, and possibly Lygns pi'at- 



