364 Lepidopterologieal Contributions. 



cimens from which Dr. Boisduval drew up his description and 

 executed his figure of Thyris vitrina, were in reality European, 

 and that Abbot's supposed drawing, as'well as any authentic 

 United States' specimens which Dr. Boisduval may have pos- 

 sessed, belong to Platythyris fasciata, nob., which, while appa- 

 rently very amply distinct, may be considered as representing 

 the European P. vitrina, in America. As is the case with 

 Thyris, our genus would then be represented on both con- 

 tinents. 



The elimination of Platythyris, draws our attention to the 

 plasticity of thoracic structure in the group to which, together 

 with Thyris, Illiger; this genus belongs, and which group it may 

 not be improper to consider as a Family — Thyridae — until 

 instituted comparisons shall have indicated its fusion with one 

 or the other already acknowledged and extensive families with 

 which it shows assimilative characters. The highest genus — 

 Thyris — imitates very plainly the higher Aegeriidae (Sesiidae) 

 in its thoracic characters ; on the other hand, the lowest 

 genus — Platythyris — resembles, in the structure of the same 

 parts, the lower Zygaenidae, especially the inferior Castniid 

 genera, Alypia and Eudryas, particularly the former. Indeed, 

 though with certain general characters in common, the two 

 hitherto established genera of Thyridae are strongly dissonant, 

 and the family may not be unadvisedly divided into two Tribes, 

 as follows : 



A. Thorax rounded in front, produced for half its length in 

 front of the insertion of the wings; antennae fiexuous, stout, 

 and slightly swelled. — Thyrini. 



B. Thorax square in front, very slightly produced; antennae 

 straight and strictly filiform — Platythyrini. 



In Thyris, the head is elevated, and received on the rounded 

 and nan-owing thoracic parts with but slight apparent contrac- 

 tion, in all of which caputal and thoracic structural points it 

 is opposed to Platythyris. In these two genera we have the 

 essential features of a group of Lepidopterological forms which 

 oscillates between Aegeria on the one hand, and Zygaena on 



