36 A CONTRIBUTION TO THE KNOWLEDGE OF 



Third stage ? Differing from the preceding in having the anal cleft 

 deeper (much as in adult) and in having spines along a portion of the 

 margin anterior to the chitinized portion of the abdomen. 



Fourth stage ? Differing from the preceding chiefly in having a 

 double or even triple row of spines along the entire margin of the body 

 anterior to the chitinized portion of the abdomen. 



Notes: This differs from A. calif arnica (Ehrh.) in numerous details, but 

 most conspicuously in having the marginal spines rounded at the tip and not acorn 

 or "spearhead-shaped" and in the wrinkled appearance of the chitinized portion of 

 the abdomen. Through the kindness of Professor G. A. Dean of the Kansas State 

 Agricultural College I have been enabled to examine a slide of A. obscura (Par- 

 rott), which appears to differ from A. ariditatis in the entire absence of marginal 

 spines. This is the third species of this genus to be described from North America. 



Genus PULVINARIA Targ. 



Pulvinaria bigeloviae Ckll. 



Fig. 16. 



Type host and locality. From Chrysothamnus (= Bigelovia) sp., 

 West Cliff, Colo. 



Material examined. From Chrysothamnus sp., between Datil and 

 Quemada, N. Mex. 



Habit. Forming a white, rather irregular and somewhat fluted, 

 slender ovisac, 5 to 10 mm. long ; ovisac not covering the dorsum ; insect 

 much shriveled when dry. 



Morphological characteristics. Length (flattened on slide) 3 to 4 

 mm. Form broadly oval. Derm membranous throughout, not pig- 

 mented. Stigmatic depressions almost or quite obsolete, and without 

 differentiated spines, their position indicated merely by the pores of the 

 stigmatic furrows. Marginal spines (Fig. 16C) small and slender, 

 arranged in an irregular series. Anal cleft of ordinary depth. Anal 

 plates (Fig. 16F) presenting no unusual characters; with four apical 

 setae, which are close to the tip, two subapical setae and two fringe setae 

 on each side, the outer of each pair the larger. Antennae (Fig 16E) 

 normally eight-segmented. Legs well developed, the tarsus (Fig. 16B) 

 curved, slightly shorter and somewhat narrower than the tibia. Digi- 

 tules of the claw slender, but little expanded at the tip. 



First stage larva (Fig. 16D) without stigmatic spines; marginal 

 spines few, extremely minute; antennae (Fig. 16A) rather stout. 



Notes : In the absence of differentiated stigmatic spines in both larva and 

 adult this species departs from the usual characters of Pulvinaria. 



