It has for some time been realized that the genus Pyrausta as it stands in current North American lists is a very unnatural one. Forbes (1926) pointed out that a fundamental division of the Pyraustinae possible on the basis of the presence or absence in the male fore wing of the frenulum hook, and that species of both types have ordinarily been included in Pyrausta. Subsequent studies of genitalic structure—particularly that by Pierce and Metcalfe (1938)—have borne out the importance of this division.

One of the most essential procedures in the identification of many Lepidoptera is an examination of the genitalia, and for a most critical examination of these organs slide mounts must be prepared. In many cases, the preparation of slides is one of the most neglected arts in lepidopterology. This is to be deplored, for a well-prepared slide is not only handsome but also much more valuable taxonomically than a messily prepared one. For large and medium-sized specimens, I have found the following technique very gratifying in producing slides of uniformly high quality. Certain phases of the technique are not particularly well adapted for working with smaller moths.