SUBFAMILY MONOPHLEBINAE 65 



antennae and the long prominent chalazae will serve to distinguish 

 them. The number of antennal segments varies with the genus 

 and in many cases even with the species. 



The female nymphs of the second stage of purchasi are difficult 

 to recognize because of the variation in their size. The antennae 

 instead of being articulated to the margin of the body as in the 

 first nymphal stage are articulated to the ventral aspect. They 

 consist of the same number of segments, six, but the fourth and 

 fifth segments are of the same length and much shorter than the 

 other segments. The cerores are more numerous and, because of 

 the more numerous longer chalazae, the segmentation is more 

 difficult to determine. The cerores and chalazae are more 

 prominent near the margin of the body. While the swellings of 

 the anal chalazae are easily identified, their setae are only slightly 

 longer than the other setae. The thoracic and abdominal spiracles 

 are similar in number and position to those of the first nymphal 

 stage. There is a small round projecting area on the meson of the 

 ventral aspect of the caudal end of the body. This structure is 

 a discaloca and appears to be wanting or is only imperfectly 

 developed in the first nymphal stage. 



The female individuals of the third nymphal stage, because 

 they intergrade in size between the large individuals of the second 

 nymphal stage and the small adults, are also difficult to identify. 

 The antennae have more than six segments, typically nine, but 

 individuals with seven or eight are not uncommon. A difference 

 in the number of segments of the two antennae of the same indi- 

 vidual is not unusual. The number of chalazae and cerores is 

 greatly increased. They are arranged in a distinct band around 

 the margin of the abdomen. The six anal chalazae can only be 

 identified with difficulty. The thoracic and abdominal spiracles 

 are similar in number and position. The spiraculariae are dis- 

 tinct. The rectal tube is trumpet-shaped in this stage and the 

 rings of anacerores, if present, have not been identified. The 

 discaloca is large and distinct. There is a smaller but similai 

 structure located on each side of the mesal discaloca. The mesa! 

 structure may be known as a mesodiscaloca and each of the others 

 as a latadiscaloca. The form of the discalocae has been used by 

 some systematists in differentiating spediies of this and pther 

 genera. They have designated them as the vaginal discs, the 

 vaginal areoles, the ventral scars, and the subcircular scars. 



The addlt females of purchasi are easily recognized by the 



