€anat(i.in mutomotmii$t. 



Vol. XLIII. 



LONDON, xMARCH, 191 1 



No. 5 



GEOMETRID NOTKS ON THE GENUS HYDRIOMENA, HUB. 



BY L. W. SWETT, BOSTON, MASS. 



As 1 was uiuible to identify material in this group, and realizing ihat 

 the species were badly mixed, I decided to try to straighten them out. 

 First, I was puzzled by the marki igs, I could find little constancy and 

 every style of variation ; secondly, in similarly marked species evtry 

 variety of colour occurred, which made the specimens so different looking 

 that I did not dire call them the same. Starting wich the first species of 

 Hydriomena in Dyar's List, namely, Hydriomena S07-didata Fab., I was 

 struck with the variability of colouring and markings, and realized that I 

 mu>t depend on something more constant than markings to separate such 

 an unwieldy mass of specimens. The genitalia, an important character, I 

 vv.is unible to study much, as most of the material at my disposal was 

 loaned, so tliat I could not proceed very far, but I noiiced that the palpi 

 cf certain species seemed to be of approximately the same relative length, 

 j.l i)vving for variation in size of specimens. This srt me on the light p.it'i, 

 as I found that by grouping certain species with palpi of the same length 

 f could follow the variations in colour, and that there seemed to be a 

 regular colour scheme in variable species, so that by knowing the colour 

 of the type ?]3ecimen I could predict the variations to a ceita n extent tliat 

 ought to (jccur under the species. The colour scheme suggested itself to 

 me from a French author's work on another group, and I found I cou'd 

 apply it here. Hydriom(7ia sordidata Fab., or more \)XQ)\)^x\y furcat i 

 Thunberg, Diss. Lis. Suec , pt. i, Dec. \\, 1784, has priority over 

 sordidata Fab., Ent. Syst., HI, pt. 2, p. 1S5, 1794, which my kind frien<', 

 Mr. Louis Prout, first points out in the Entomologists' Record (London). 

 Vol. 9, p. 84-87, April, 1S97. Hydriomena sordidata Fab. does not 

 become a synonym, as it is a green variety o^furcata Thunb., and should 

 be listed so. An excellent figure o{ fur cat a is given, tab. 3, No. 10, and 

 it is strange that the older authors did not recognize this. The colour 

 scheme of Hydriomena fnrcata I hunb. is as follows, and ai)plies to the 

 other variable species : i, cinereous or gray ; 2, greenish ; 3, reddish ; 4, 

 yellowish ; 5, suffused ; 6, mesial space white. 



