137] LEPIDOPTEROUS LARVAE— FRACKER 137 



Head about as large as prothorax, not retractile except in Phoebis, 

 distinct from prothorax and with caudal half well developed ; front 

 extending about half way to top of head ; labrum moderately emarginate ; 

 numerous secondary setae present, varying from minute to large and 

 borne on papillae of various sizes ; surface of head varying from nearly 

 smooth to rugose and irregular. Body bearing numerous secondary 

 setae, sometimes all similar, usually of widely different sizes and borne 

 on chalazae varying from microscopic to conspicuous; segments divided 

 into annulets, usually six in number, each annulet bearing either a 

 single row of setae or a band nearly its full width. Prolegs present on 

 segments 3, 4, 5, 6, and 10, all similar in size; crochets biordinal or 

 triordinal, always arranged in a mesoseries. 



The following synopsis includes six of the nine genera occurring 

 north of Florida and east of Texas and the Rocky Mountains. No 

 specimens of Nathalis idle, Zerene caesonia, or Pyrisita mexicana of the 

 southern states have been available. Larvae of all of the northern 

 species east of the Rockies have been examined except Eiirymus interior. 



Genera of Pieridae : 



a. Setae of head borne on chalazae, those of front much smaller than 

 those laterad of the epicranial suture. 

 b. Head with many chalazae as high as tubercles on which ocelli are 

 placed, about as conspicuous as those of thorax. 

 c. Prothoracic legs at least half as long as mesothoracic. Pontia 



cc. Prothoracic legs much less than half as long as mesothoracic. 



Callidryas 



bb. Head with chalazae usually lower than ocellar tubercles; when a 



few are well developed they are not one-fourth as large as those 



of prothorax. Synchloe 



aa. Setae of head usually not borne on chalazae, those of front always 



similar to those laterad of the epicranial suture; setae of body all 



minute and similar. 



b. Head about one-third as wide as abdomen, deeply retractile. 



Phoebis 

 bb. Head at least half as wide as abdomen, scarcely retractile. 



c. Body setae not on chalazae or on very small ones. Eiirymus 



ec. Body setae borne on distinct chalazae, higher than wide. 



Eu re ma 

 Pontia monuste and Pontia protodice have many of the chalazae 

 much larger than others, while P. rapae and P. napi (including var. 

 oleracea) usually have all the chalazae small and subequal in size. 



Neither of the two species of Callidryas have been available but the 



