GeoiTietndse 



Larvce with the three anterior pairs of abdominal claspers to- 

 tally aborted, and progressing by bringing the posterior somites 

 close to the thoracic, looping the medial somites. In a few an- 

 cestral forms there is tendency to develop additional prolegs and 

 to a more ordinary mode of progression." 



The larvae, which are commonly known as "measuring- 

 worms," "span-worms," or " loopers," have the power in many 

 cases of attaching themselves by the posterior claspers to the 

 stems and branches of plants, and extending the remainder of the 

 body outwardly at an angle to the growth upon which they are 

 resting, in which attitude they wonderfully resemble short twigs. 

 Dichromatism is often revealed among them, part of a brood of 

 caterpillars being green and the remainder brown or yellowish. 

 Various explanations of this phenomenon have been suggested. 

 In not a few cases the females are wingless. 



Over eight hundred species of Geometridce are known to 

 occur within the limits of the United States and Canada, and 

 when the region shall have been exhaustively explored, there is 

 little doubt that this number will be greatly increased. It is im- 

 possible within the limits of this book to mention and depict all 

 of these species. We have therefore confined ourselves to the 

 description through our plates of one hundred and seventy spe- 

 cies, which are either more commonly encountered, or are pos- 

 sessed of some striking character. Incidentally occasion has been 

 taken to figure a few of the types of species in the collection of 

 the author which have never before been delineated. 



The student who desires to fomiliarize himself with the fam- 

 ily with which we are now dealing will derive much assistance 

 from the writings of Packard and Hulst, the titles of which he 

 will find in the portion of the Introduction of this book devoted 

 to the literature of the subject. 



SUBFAMILY DYSPTERIDIN^ 

 Genus DYSPTERIS Hiibner 



(i) Dyspteris abortivaria Herrich-Schc-effer, Plate XLII, Fig. 

 21, 3. (The Bad-wing.) 



This pretty little moth may be easily recognized by the fact 

 that the hind wings are so much smaller than the fore wings. 



3^3 



