13 
Representative Species. 
By Prof. A. RADCLIFFE GRoTE, A.M. ead by J. W. TuTTt, F.E.S., 
on March 25th, 1897. 
Tue Noctuid fauna of North America is composed of (1) a 
palearctic element showing affinities with the European fauna of 
to-day ; (2) an original North American element ; and (3) a tropical 
American element intrusive from the south. The latter makes itself 
felt to a considerable extent, owing to the fact that there is a con- 
tinuous land connection with the tropics through Mexico ; while the 
proximity of the West India Islands to the Gulf Coast, the prevalence 
of winds from south to north during the summer, the presence of the 
Gulf Stream, and the circumstance that the extremity of Florida on 
the one hand, and a portion of ‘Texas on the other, belong in reality 
to the American tropical region, facilitate its spreading over the 
North American continent. To the phenomena offered by this 
tropical element of the North American Noctuid fauna I have 
devoted much attention, particularly in relation to Aleta argillacea, 
the so-called cotton-worm, which I have shown to have been 
originally introduced from tropical America, and which still con- 
tinues yearly to invade our territory. This element, of whose 
constituent species I have given partial lists, need not detain us 
here. As compared with Europe the tropical element is much more 
important in North America, owing to the absence of a dividing sea 
like the Mediterranean, and to the unbroken extension of the land 
masses to the south. The purely North American element consists 
of the peculiar genera. Their sorting out is to some extent a matter 
of opinion. The theory with regard to this element is that it 
originated on North American territory, and is the survival of pre- 
glacial ancestors. The first and largest element, however, is the 
paleearctic, which, allied throughout structurally to the European 
Noctuids, affords a greater number of species readily to be dis- 
tinguished from their congeners in the Old World. It is assumed 
with regard to this element that it is descended from a common 
pre-glacial circumpolar or northern fauna which flourished, with local 
modifications, but more or less uninterruptedly, over the Northern 
Hemisphere before the setting in of the first ‘ice age.” The change in 
climate drove the species then inhabiting North American territory 
slowly to the south, the cold climate still lingering in the north, 
interposing a permanent barrier on both sides to a further mingling 
of blood. Henceforward the American Noctuids belonging to the 
former circumpolar fauna were left to themselves, and the changes 
