THE DISTRIBUTION OF CALIFORNIAN MOTHS. 457 
the European fauna in that of California. Here I think Dr. Gray 
has been the first to indicate a solution of the problem. Our 
knowledge of American fossil tertiary insects is at present almost 
nil; we must, then, in the absence of any evidence to the con- 
trary, follow the conclusions of Gray with the later confirmation 
of Heer and Lesquereux. 
The ancestors of the Californian Parnassius, Rhaphidia and 
other European forms, may have inhabited the Arctic tertiary con- 
_ tinent, of which Greenland and Spitzbergen are the remains, and 
their descendants forced southward have probably lost their foot-, 
hold in the Atlantic region and survived in California and Europe, 
like the Sequoia in California. Something more than similarity of 
climate is needed to account for the similarity of generic forms ; 
hence community of origin, with high antiquity and a southward 
migration of forms not of tropical origin, are the factors needed 
to work-out the problem. That something of this sort has taken 
Place in marine animals we know to be the fact. Certain forms 
now supposed to be extinct on the coast of New England and 
Scandinavia, such as Yoldia arctica Gray (Nucula Portlandica 
Hitchcock), are still living in the seas of Greenland and Spitz- 
bergen. The quaternary fauna of Maine indicates a much more 
purely arctic assemblage than is at present to be found. This is 
also the case with the Scandinavian quaternary fauna, according 
to the researches of Prof. M. Sars. As we have before shown, the 
cireumpolar marine fauna runs down along the coast of north- 
eastern America and of Europe, and the forms common to the 
two shores have not come one from the other. Europe has not 
Perhaps borrowed in quaternary times from America, but both 
have been peopled from a purely circumpolar fauna. If there has 
n any borrowing it has been on the part of Europe, since the 
fossil musk ox of France and central Europe is said to be identical 
With the musk ox of arctic America. So also on the coast of 
northeastern Asia and Alaska are circumpolar forms, which have 
evidently followed the flow of the arctic currents down each coast. 
forms which are identical or representative on these two coasts 
are forms derived from the circumpolar fauna; so the forms which 
are so strikingly similar in northern Japan to those on the coast 
of New England are, if we mistake not, also derived from the 
northward. I believe it to be a matter of fact that the Atlantic 
tates species of insects which are common to the two countries, 
