8 THE ENTOMOLOGIST S BECOBD. 



On an yidditioiial JVIetliod for Determining the Species of 

 certain Lepidoptera. 



By W. S. RIDING, M. D. 



It has frequently occurred to me that the structure of the scales of 

 Lepidoptera might be a helj) in the classification of certain species, 

 which, at present, afford considerable difficulty. Some time ago I 

 examined the subject cursorily with reference to the closely allied 

 varieties of Orrhodia vaccinii and 0. ligula, especially vars. rtifa (Tutt) 

 and spadicea (Hb.) of the former, which have the characteristic 

 apex and hind- margin of ligula, a good many of which are taken here. 

 I have long considered these as vars. of ligula, but the general feeling 

 of lepidopterists seems to be against this view and such specimens 

 have, I believe, been accepted for the most part as varieties of vaccinii. 

 Kecentlyl have again gone into the question, with the result of confirm- 

 ing my previous imi^ression. I find the scales of the upper surface of 

 the forewings of the types of vaccinii and ligula jDresent a constant 

 difference, and that the special varieties alluded to should be placed, from 

 this point of view, under the species ligula and not under vaccinii. 



In the first place, I examined with a microscope a tyj^e specimen 

 of 0. vaccinii (ochreous, with brown markings and pale wing rays), 

 taking some scales from the base, middle and hind margin of the upj^er 

 surface of both fore-wings. These I found to vary in the number of 

 teeth, some having 3, others 4, 5, or 6. I added together those having 

 a similar number and took the percentage, with the following result — 



Scales with 3 teeth formed 15 per cent, of the whole. 



55 ^ 55 55 ■'-■^ 55 » 



fi 4 



55 'J 55 55 ^ 55 55 



100 



or, 84 per cent, of the scales of typical vaccinii were found to have 3 or 

 4 teeth. I then took the scales of a typical 0. ligula (var. ochrea, Tutt), 

 our common form here, which has a yellowish band before the hind 

 margin, and found that there were no scales with 3 teeth but that — 



Scales with 4 teeth formed 15 per cent, of the Avhole. 

 ^ 44 



55 " 55 55 ^^ 55 55 



55 " 55 55 ^^ 55 »> 



7 ^ 



55 • 55 55 " 55 55 



100 



or, 85 per cent, of the scales of typical ligula had 5, 6, or 7 teeth. 

 These data were confirmed by a general examination of many other sjieci- 

 mens, with an approximately similar result. We may thus, apparently, 

 distinguish typical 0. vaccinii from 0. ligula by the large predominance 

 of scales with 3 or 4 teeth (about 84 per cent.) in the former, and 

 of scales with 5, 6, or 7 teeth (about 85 per cent.) in the latter. A 

 glance at the field under the microscope is sufficient to do this. 



My attention was next directed to ascertaining whether this fact 

 would help us in determining the species of the varieties (hitherto 

 classed as vaccinii), rufa (Tutt) and spadicea (Hb.), having a pointed apex 



