16 
EUROPE. NorTH AMERICA. 
flyppa rectilinea, Esp. Flyppa xylinotdes, Gn. 
Achatia atriplicis, L. Achatia delicata, Grt. 
Fleliophila lithargyria, Esp. Fleliophila pseudargyria, Gn. 
Pyrophila pyramidea, \.. Pyrophila pyramidoides, Gn. 
Cucullia umbratica, L. Cucullia intermedia, Spey. 
Plusia festuce, L. Plusia putnamt, Grt. 
Fleliothis dipsaceus, L. Flehiothis phlogophagus, G.and R. 
Catocala fraxint, L. Catocala relicta, Walk. 
Catocala pacta, L. Catocala concumbens, Walk. 
p) 
This list of ‘“ representative” species might be extended. The 
resemblances are of different degrees of intensity. ‘The two species, 
NV. augur and WV. haruspica seem chiefly to differ in the structure of 
the ¢ genitalia. The variability of the ¢ genitalia within the limits 
of a single species is not ascertained. If, as has been asserted of 
Bombus, the peculiar construction of the genitalia (hereof the ? ) 
is such as to present effective copulation between otherwise allied 
species, the value of the genital structures as a whole has hitherto 
been underrated by entomologists. On the other hand, as a syste- 
matist, I should object to according generic value to modifications of 
the genitalia as a decisive character, for the reason that otherwise 
closely related owlet moths are found to have very different types of 
genitalia, while practically the formulation of the different types 
seems exceedingly difficult. ‘The genitalic character is now being 
used with apparent success to separate species which run so 
closely as to make their distinction on other grounds practically im- 
possible. 
The theoretically “representative” species must evidently be the 
changed descendants of a common ancestor, now widely separated 
in space, distributed over different geographical regions whither they 
were brought by natural forces, change of climate inducing migration, 
cataclysms effecting sudden separation. In the present case we may 
often have to do with merely parallel species which have ceased to 
perpetuate themselves in North America or Europe. Deeper studies 
and comparisons of minute variations in structure may lead to 
important generalisations, and to additions to the general theory 
which is here presented in outline merely, and which simply accounts 
or tries to account for the existence of identical and ‘representative ” 
species of owlet moths in Europe and North America. Carried into 
other groups, the same general phenomena present themselves. In 
the Platypierygide our few species of ‘hook-tips” are all of the type 
of the European Platyptervx falcataria, L. The hamutla type, typical 
of the generic term, is not represented with us. We have one species 
allied to Prionia lacertinaria. Cilix is wanting in the North 
American fauna, while we have two species of the Northern Asiatic 
genus Orveta (Dryopterts), all telling of former relations which have 
