THE CANADIAN ENTOMOLOGIST. 69 



mode of its attachment to the thorax, it attains a higher vahie. The head 

 is sometimes free, separated from the thorax by a distinct constriction, 

 and sometimes it is closely applied to it and almost buried in its vestiture. 

 This about exhausts the head, and it will be seen that by the variations 

 of the head and its appendages alone, numerous divisions and subdivisions 

 can be established, which will simplify the determination of unknown 

 species. 



The tJwrax and its appendages vary less, but even here there is a great 

 deal of difference. 



In shape it is usually convex, sometimes very large and heavy, rarely 

 small ; often it is somewhat depressed and occasionally quite flat ; some- 

 times it is quadrate, but more usually rounded or ovate. Alone these 

 variations do not present good generic characters, but combined with 

 tuftings and the proportion the thorax as a whole bears to other parts, 

 they afford good distinguishing features. 



The vestiture is usually hairy, often scaly, and sometimes a mixture of 

 both. The extremes would be generically distinct, but where the vestiture 

 is mixed, the question is not free from doubt ; ordinarily an insect with 

 mixed vestiture would be distinct from either a hairy or a scaly one, but 

 sometimes the mixture is so slight, or the hairy insect has the hair so 

 much flattened, that a generic separation would be unjustifiable. Acronycta 

 and Hadena each fall into two very well marked divisions by the char- 

 acter of the vestiture. 



The tnftiiigs vary considerably. Sometimes there are none, sometimes 

 there is only a small acute tuft behind the cpllar, sometimes a divided 

 crest or tuft in the same place, and again there may be a rounded or 

 truncate bunch of hair. Posteriorly there is usually a larger rounded 

 tuft, but .sometimes, as in Plusia, it rises upward saddle-shaped, or as in 

 Zale and Hovioptera, it is divided into three diverging tufts truncate 

 behind. 



The cotlar is sometimes produced at the middle, and excavated at 

 either side, sometimes flat, disk-like, or again, as in Cucullia, hood-like 

 and exaggerated. 



These modifications of tufting and collar have but a small generic 

 value. The presence or absence of either, or the variations in form, 

 would not indicate a generic difference, though a total absence o tufts 

 would probably do so if there were no intermediate forms. 



The tibia are sometimes spinose and sometimes not. This affords an 



