Distribution of Moths of the Sub-family Bistonince. 255 



could be gained. Even then, any interchange between Africa 

 and Europe was but slight and, had an easy crossing been 

 possible, the Sahara Desert would have been hopeless as a 

 refuge for temperate forms. 



Throughout the Glacial Period, crowds of refugees suc- 

 cessfully lived far from glacial conditions in Japan, China, 

 Mexico and the Southern United States. It is necessary to 

 note, however, that the Asiatic sanctuary, on account of its 

 great southward extension, its warm Japanese current, its 

 more decidedly insular climate, sheltered a great many more 

 forms than did Eastern America. In consequence, even in 

 the latter area, many species like the Maiden Hair Tree ( Ginkgo 

 biloba), once ubiquitous (as the fossils indicate), have died out, 

 and yet have survived in Asia. 



Here a new problem crops up. Had all of these surviving 

 forms common to the American and the Asiatic areas been 

 continuous right across America from the Atlantic to the Pacific 

 Ocean, we should have attached no great significance to the 

 discontinuity of the Asiatic and American habitats. We 

 should have concluded that, in all probability, we were dealing 

 with very early Quaternary Asiatic immigrants of the same 

 group as such palpably Palaearctic invaders as Papilio zolicaon, 

 Thecla (Callophrys) dumetorum and Saturnia mendocino, now 

 domiciled in Pacific North America. But, strange to say, 

 none of these Tertiary relicts common to America and Asia 

 appear in California, Oregon, Washington and British Columbia. 

 Not only do these groups fail, but indeed extremely few forms 

 are common to Pacific and Atlantic America ; in fact, the whole 

 aspect of the two Floras and Faunas is totally dissimilar. 



It seems, at first sight, that we have on the West coast 

 the same conditions postulated as likely to favour Tertiary 

 survivors. We have the same north and south trend of the 

 mountains, the same coast conditions and the same insular 

 climate. This summary of phenological conditions assumes, 

 however, that the Pacific Coast of to-day and that of later 

 Tertiary times were much the same. As a matter of fact, 

 I believe that the coast line of that region, in Miocene and earlier 

 Pliocene times, approximated to a line just west of the Rocky 

 Mountains ; all that existed of the coast states was a peninsula 

 jutting out westward from Wyoming and Colorado. Only by 

 this route was access for Eastern species to the Californian 

 area possible. This explains the paucity of such forms as 

 Platysamia rubra (representative of the Eastern P. cecropia) 

 and Telea polyphemus, west of the Rockies, and shows why 

 Sequoia, which revels in a very moist climate, persists in the 

 west and not in the drier regions to the east of the barrier. 

 Any great use of the gateway to the Pacific was an impossibility, 

 for prairie and desert conditions, as well as the mountain 



1917 Aug. 1. 



