314 ENTOMOLOGY 



Patagonia; and Megilla maculata from Vancouver and Canada to Chile. 

 About six hundred species of beetles are holarctic in distribution, as was 

 mentioned. Some of them inhabit different climatal regions in dif- 

 ferent parts of their range; thus Melasoma (Lino) lapponica in the Old 

 World " occurs only in the high north and on high mountain ranges, 

 whereas in North America it extends to the extreme southern portion 

 of the country," being widely diffused over the lowlands (Schwartz). 

 Similarly, Silpha lapponica is strictly arctic in Europe, but is distributed 

 over most of North America; Silpha opaca, on the contrary, is common 

 all over Europe, but is strictly arctic in North America. Silpha atrata, 

 common throughout Europe and western Siberia, was introduced into 

 North America, but failed to establish itself. 



Southwest. Very many species have come to us from Central 

 America and even from South America. South America appears to be 

 the home of the genus Halisidota, according to Webster, who has traced 

 several of our North American species as offshoots of South American 

 forms. Many of our species may be traced back to Yucatan. H. cinc- 

 tipes ranges from South America to Texas and Florida; H. tessellaris 

 has spread northward from Central America and now occurs over the 

 middle and eastern United States, while a form closely like tessellaris 

 ranges from Argentina to Costa Rica; H. caryce follows tessellaris, and 

 appears to have branched in Central America, giving off H. agassizii, 

 which extends northward into California. Similarly in the case of the 

 Colorado potato beetle (Leptinotarsa decemlineata) and its relatives. 

 According to Tower, the parent form, L. undecemlineata, seems to have 

 arisen in the northern part of South America, to have migrated north- 

 ward and, in the diversified Mexican region, to have split into several 

 racial varieties. The parent form grades into L. multilineata of the 

 Mexican table lands, which in turn, in the northern part of the Mexican 

 plateau, passes imperceptibly into L. decemlineata, which last species has 

 spread northward along the eastern slope of the western highlands, west 

 of the arid region. In the lower part of the Mexican region the parent 

 form may be traced into L. juncta, which has spread along the low humid 

 Gulf Coast, up the Mississippi valley to southern Illinois, and along the 

 Gulf Coast and up the Atlantic coast to Maryland, Delaware and New 

 Jersey. In general, the mountains of Central America and Mexico and 

 the plateau of Mexico have been barriers to the northward spread of 

 many species, which have reached the United States by passing to the 

 east or to the west of these barriers, in the former case skirting the Gulf 

 of Mexico and spreading northward along the Mississippi valley or along 



