70 ILLINOIS BIOLOGICAL MONOGRAPHS [70 



Scythridinae 



a. Crochets biordinal, arranged in a complete uniserial circle. Scjjthris 



Yponomeutinae 



a. Pi group on metathorax consisting of two setae. 



b. Crochets arranged in a mesoseries. 3Iieza 



bb. Crochets arranged in a miiltiserial circle. Atteva 



aa. Pi group on metathorax consisting of a single seta ; crochets arranged 

 in a multiserial circle, 

 b. Cephalic seta of Kappa group on prothorax ventrad of the other 

 two. 

 c. Beta ventrad of alpha on metathorax; segment 9 with a dorsal 

 shield bearing setae alpha, beta, rho, kappa, and eta. 



ZeUeria 



ec. Beta caudad of alpha on metathorax. Swammerdamia 



bb. Cephalic seta of Kappa group on prothorax dorsad of the other 



two ; beta caudoventrad of alpha on metathorax. Yponomeuta 



The following species of Yponomeutidae were examined : 

 Plutella maculipemiis Cerostoma ruhrella 



Schreckensteinia erythriella Scythris magnatella 



Mieza igninix Atteva aurea 



ZeUeria gracilariella Swammerdamia pyrella (Europe) 



Yponomeuta plumhella, Y. muUipunctella 



Family Gracilariidae 



The gracilarians form one of the most definitely bounded families 

 of the order. Whether examined in an early or a late instar, they are 

 distinct from the larvae of other moths. This is true in spite of the fact 

 that a complete change of structure takes place at the second or a later 

 molt. Before this molt the mandibles are horizontal and wheel-shaped, 

 and toothed like a buzz-saw. No such structure is known elsewhere. 

 The distinctive feature of the later instars is the presence of but three 

 pairs of ventral prolegs, located on segments 3, 4, and 5. It should be 

 noted that where the number of prolegs is reduced in other families, as 

 in some Noctuidae, Geometridae, and Nolidae, they are always present 

 on segment 6 and are first lost on segment 3. The prolegs of gracilarian 

 larvae are very short and are often not represented by swellings at all 

 but their location is shown by suckers or by crochets which are arranged 

 in various ways. Thoracic legs may be present or wanting. The setae 

 are so minute that their position usually can not be determined satisfac- 

 torily. 



