( cxvii ) 



The difitributioii of ilic Hawk Moths of North America illustrates a marked 

 fouuistic division of the Continent into an Atlantic and a Pacific Subregion. 

 The Atlantic Subregion reaches westwards to the Mississippi plains and includes 

 part of Texas. It contains far more Neotropical immigrants than the Western 

 Subregion, Florida offering special facilities for a northward migration of the 

 Neotropical Splunt/iilae of the West Indies, none of the Neotropical species 

 wliich occur regularl}- or occasionally in (ieorgia, Carolina, etc., being absent 

 from Cuba. The genera characteristic for tlie Atlantic Subregion are thirteen: 

 Dolba, (/I'ratoi/i/'f, Isogramina, Isoparce, Atreus, lAipara, Ampeloeca, Darapsa, 

 De'idamia, Ampfiion, Calasi/mholus, and Cressonia, besides Sp/iecor/i/ui, which 

 occurs, however, also in the Pacific district of the Palaearctic Region. The 

 Atlantic Subregion is, therefore, rich in genera peculiar to itself, while the 

 Pacific side of the Continent, from the Rocky Mountains to the Pacific Ocean, 

 has only three genera restricted to itself {Arcfouotus, JiJiiproserjjuiiis, antl 

 l)tct</osom((). Of these western genera, Arctonotus and Euproserpinus are 

 derivations fiom Proserpinus, and Dlctijosoma from the Atlantic Ceratomia. 

 The two Pacific species of Proserpinus and the only European one are more 

 specialised than the two species which belong to the Atlantic Subregion. We 

 have, therefore, the remarkable fact that what is characteristic for the Nearctic 

 Region is essentially Atlantic. The Atlantic Subregion is the birthplace of the 

 Nearctic Sphingid fauna. This is borne out by the two Holarctic genera S/ihinx 

 and Ilaemorrluigia, which have together five species in the Atlantic and only 

 two in the Pacific Subregion of North America. This distribution gives a hint 

 how to explain the glaring contrast existing between temperate aud tropical 

 America in the Sesiinae aud C/toerocampinae. One would have expected to find 

 that, as is the case in Aclierontiinac, the large Neotropical stock of Sesiinae 

 had given rise to a crop of Nearctic specialisations, and tliat the Choerocamjiiue 

 genus Xi/lojihanes, flourishing with fifty species in the Neotropical countries, 

 had some special representatives in temperate North America. Temperature 

 and other atmospheric factors as such cannot be the cause of the deficiency in 

 the North American fauna, since the Sesiine genus Ihiemori'hagia is almost 

 exclusively an inhabitant of the northern temperate countries of the Old and 

 New Worlds ; since, secondly, the Palaearctic Region has eight species of Choero- 

 campinae to itself, besides Pergesa elpeyior, which reaches into India ; since, 

 thirdly, temperate South America has several Sesiinae and Choeroeampinae which 

 do not go far north into the tropics ; aud as, fourthly, the tropical plains as well 

 as the temperate high mountainous districts of South and Central America are 

 inhabited by Sesiinae and Choeroeampinae. However, if it is hardly possible that 

 conditions of life are at the root of the discrepancy, the paucity of Sesiinae 

 in North America and the al)S('nce of any indigenous si>ecies of Choeroeampinae 

 from that Region must find an explanation in the geograpliical history of the 

 Western Hemisphere. The explanation is rendered complicated by the fact 

 that there are no less than seven purely Nearctic genera of Acherontiinae 

 which are of Neotropical extraction, and therefore apt to contradict any likely 



