66 



species is darker by a larger proportion of black ; even the pat- 

 tern (the lunules and arrow lines) is often more strongly 

 developed in American species by being of a deeper black. The 

 transverse lines and the spots are more visible by having 

 stronger blackish borders. 



In the colors made of a mixture of yellow and red, Dr. 

 Speyer observed just the opposite change. In the American 

 species the red is predominant and the black more evanescent 

 ( Orthosia ferrugineoides, Hydroecia nictitans, Plusia Putnami^ 

 Brephos inf arts'). 



The difference in the shape of the wings, if present, consists 

 mostly in the American species having broader and shorter 

 wings. 



Dr. Speyer believes that the modification in the mixture of 

 the grayish and reddish colors is alone of importance, as he 

 observed it, with few exceptions, in the larger part of the species 

 compared. 



He is not certain about the cause which produces the fact, 

 but he believes that the two climates of America and Eiirope 

 are well represented by the fact. It is generally observed that 

 the color grows darker and more blackish to the north or at 

 higher elevations, but it is not certain whether this is produced 

 by the stronger and colder winter, as in some species ( Vanessa 

 prorsa, Pobjommatus Phlaeas) it is the summer generation 

 which is more blackish. 



Dr. Speyer considers the climate of Europe as presenting a 

 more insular character, the climate of America a more conti- 

 nental character. The fauna of Siberia should have nearly the 

 same difference from that of Europe as the fauna of America 

 has, but the fauna of Siberia is still too imperfectly known to 

 allow of sure conclusions. The little that is known of it, how- 

 ever, is in favor of Dr. Speyer's remarks. Nearly all the 

 species which he was able to examine came from the eastern 

 part of the Union ; perhaps the fauna of the western parts 

 would give a more conclusive result. 



A difficulty in the exact comparison of the North American 

 and European species consisted in the fact that most of the 

 American Noctuina were specimens collected in the field, 



