specimens from the Hy. Edwards, Grossbeck and Pearsall Collections, 

 has proved of enormous value to us in determining the status of obscure 

 forms. 



We might note that we have found it extremely difficult to accur- 

 ately identify some of the older names, notably those of Packard, on 

 account of the types being almost invariably $ 's and furnished with 

 very inadequate locality labels ; this, combined with the fact that several 

 species which show an extraordinary difference in the shape of the S 

 Uncus, are superficially extremely alike, renders this group one of the 

 most perplexing among the Nortli American Geometridac. 



We retain the palpal subdivisions as proposed by Mr. Swett and 

 consequently in the main his sequence of species ; we illustrate our con- 

 ception of each species by a half-tone figure of the insect in question 

 as well as of the S genitalia ; in instances where it has been impossible 

 to make a slide we add a text-figure of the Uncus as viewed from above 

 under a binocular microscope ; we have found the shape of the Uncus 

 remarkably constant in all species where long series have rendered it 

 possible for us to make slides of several specimens as well as to examine 

 the Uncus under the binocular ; some slight variation is naturally pres- 

 ent which we shall comment on under the various specific heads, but 

 wherever we have found a marked difference we believe the above 

 grounds justify us in treating it as of specific value. 



I. Short Palpi Group. 



HvDRiOMENA FURCAT.\ Thun. (PI. I, Figs. 1-6; PI. VII, Fig. 1). 



An excellent figure of the genitalia of this European species is 

 given by Mr. Pierce in 'The Genitalia of the British Geometridae,' PI. 

 43 ; we have made slides of European specimens and of numerous 

 specimens from various North American localities and find them 

 practically identical ; there is considerable variation in the length of 

 the lateral apical points, but this is more apparent than real as these 

 points show a tendency to curl up. The species extends along tiie 

 Pacific Coast from Alaska through British Columbia, where it is com- 

 mon, (Vancouver Island, Kaslo, Arrowhead Lake) down the Sierra 

 Nevada range into Central California (Siskiyou Co., Alameda Co.) ; 

 it also extends down the Rockies into Colorado (Calgary, Alta. ; 

 Banff, Alta.; South Park, Colo.) and we even have single specimens 

 from the White Mts., Arizona and Provo, Utah. The furthest point 



