113] LEPIDOPTEROUS LARVAE — FR ACKER 113 



are always uniordinal and the full five pairs of prolegs on segments 3 to 

 6 and 10 are always present. The notch of the labrum is somewhat 

 varied, but, as a rule, is deep, with parallel sides and a rounded bottom. 

 Twenty-two of the forty-two species of Acronycta examined appear to 

 belong in this group, as well as Charadra deridens, Panthea furcilla,. 

 Demas propinquilinea, the species of Eulonche, Simyra, Polygram- 

 mate, Agriopodes, and possibly a few other Acronyctinae. 



Group 3. Vernicae obscured by the development of secondary 

 setae. This large number of secondary setae covers all the characters 

 ordinarily used in the identification of noctuids and necessitates a 

 search to find other distinguishing structures. It happens, however, 

 that no other multisetiferous larvae have uniordinal crochets and short 

 prolegs except Datana and Melalopha of the Notodontidae, and these 

 are so distinctive in appearance that there is little danger of confusing 

 Acronycta with them. The parallel-sided notch of the labrum is also 

 distinctive*. Fifteen of the species of Acronycta examined are of this 

 type. 



Group 4. Verrucae reduced to single setae or small or indefinite 

 groups of setae in the last instar altho preceded by well developed tufts 

 in earlier stages. In accordance with a well recognized natural law, 

 degeneration of a structure does not result in a condition exactly similar 

 to that from which the structure arose. Thus the reduction of verrucae 

 to single setae almost never causes a complete return to the generalized 

 ehaetotaxy. In Lithosiidae this is shown by the double nature of Rho 

 on the abdomen and of Pi on the mesothorax and metathorax, and in 

 Arctiidae by the multisetiferous leg-plate of Doa or the bisetose Pi 

 group on the metathorax of Utetheisa. Both these latter conditions are 

 found in that anomalous, notodontid-like, noctuid genus Harrisimemna. 

 In the Acronyctas, however, the leg-plate seems to have been reduced to 

 three setae and the Pi group on the metathorax to one seta at the same 

 time that alpha, beta, rho, etc., degenerated from verrucae to single 

 setae. It is a strange fact that mu has not followed the same course but 

 retains its multisetiferous condition as a well developed verruca. This 

 is true of all the "single-haired" Acronycta larvae examined, viz., A. 

 exilis, A. haesitata, A. afflicta, and A. funeraUs. 



In any synopsis of the larvae for purposes of identification, the 

 four groups must be handled separately in spite of the fact that they 

 have all been derived from the same type. They are listed above in 



*The labrum of Acronycta leporina, which belongs here, is figured by Forbes 

 (1910) as having a shallow notch. This does not agree with the individuals of this 

 species which I have seen nor with any other Noctuidae having numerous sec- 

 ondary setae obscuring the verrucae, so far as I know them. 



