PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 



issued |^^fVA„ v)*^l ^y '^' 



SMITHSONIAN INSTITUTION 



U. S. NATIONAL MUSEUM 



Vol. 91 Washington: 1941 No. 3123 



THE NORTH AMERICAN MOTHS OF THE GENUS 

 ARACHNIS, WITH ONE NEW SPECIES 



By J. F. Gates Clarble 



The study of the genus Arachnis (family Arctiidae) was undertaken 

 to determine the exact relationship of the new species described to 

 the known species, and, in order to accomplish this, characters for 

 all species in the group needed to be critically reviewed and evaluated. 



The species of this group are extremely plastic and readily produce 

 forms and races apparently constant in coloration. These may be 

 confined to small islands within the range of the species or may occur 

 along with the typical race. 



The lack of sufficient material has probably prevented a proper 

 evaluation of characters in one or two instances, but it seems apparent 

 that at least one species, picta, has given rise to numerous varieties 

 and races that are so distinct superficially that they appear to be 

 separate species. The case of midas^ for example, is striking. This 

 so-called species, although easily distinguishable from picta on color- 

 ation, can be separated from it morphologically only by the shape of 

 the uncus. As pointed out later, midas is represented only by the 

 unique type, and the distinguishing character of the genitalia might 

 well be only one of several variations. Since the matter of coloration 

 seems to be of little importance in the separation of species, midas, like 

 citra, may be nothing more than a form or race of picta. 



The genus appears to be best represented in the southwestern part 

 of the United States, but its distribution ranges into Mexico and to 

 the Midwest and Florida. It is in the Rocky Mountain region that 



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