February, 1914 Bulletin of the Broof^Iyn Etitomological Societtf 21 



Short Studies in Geometridae : No. 2. 



By Richard F. Pearsall, Brooklyn, N. Y. 



Petrophora fluctuata, Linn. — This study was undertaken to 

 remove some doubts caused by a suggestion of one of my foreign 

 correspondents that some of our western species, so called, were 

 only overgrown forms, or races, of well known eastern types. 

 In the Canadian Entomologist, vol. 38, p. 400, the Rev. Geo. W. 

 Taylor separates two western species, theretofore confused with 

 fluctuata, under the names of pontiaria and fossaria. The former, 

 of which I have a number of specimens, is not so very unlike a 

 larger, coarser replica of our eastern form. The latter I do not 

 know. Two years later, (Can. Ent, vol. 40, p. 59) he separates 

 our eastern species under the name of planata, overlooking 

 Guenee's previous name of iduata, to which Dr. Dyar has 

 called attention (Proc. Ent. Soc. of Wash., vol. 10, p. 33). He 

 compares it with fluctuata, relying upon color differences and the 

 direction of the cross lines, a rather slender basis, as he admits. 

 Had he examined their antennal structure, figures of which are 

 here given, he would have discarded ^zidwa^a without hesitancy. 



But, it will be noted, in the American species under discus- 

 sion the antennae are alike in structure, and in order to get a 

 positive clue for separation, mounts of the O genitalia were 

 prepared, and drawings in part herewith presented, showing so 

 wide a variation that further comment is needless. A closely 

 analogous position exists between our species of Nyctohia 



Antenna (under side) of Petrophora Antenna (under side) of Petrophora 



pontiaria Taylor and P. iduata Guen. fluctuata Linn. 



