1U11] Specific Characters in Pseudococcus 327 



great as to nullify the usefulness of the character. To deter ■ 

 mine the distal termination of the setae is sometimes difficult, 

 but it can be done with considerable accuracy. Another 

 difficulty is that the distal end of the setae have a tendency to 

 curl, but in spite of this and the above mentioned factor the 

 length of a seta can usually be quite accurately measured. As 

 stated above the comparison of the length of the setae of the 

 anal ring with the setae of the anal lobes is probably the most 

 available way to use this character. 



In agrifoliae Essig considerable variation is found and the 

 character is hardly satisfactory, The setae of this species are 

 especially difficult to measure because they are not robust. 



Dermis-. — The presence of setae and groups of spinnerets 

 upon the dermis is a character commonly noted. This is 

 usually not given enough in detail to be of assistance in the 

 separation of species. 



Egg-Sac. — Considerable use is made of the egg laying 

 habits of the species. Whether the egg-sac is of a fibrous 

 nature or is a mealy secretion is often stated. Also its presence 

 or absence is noted, depending whether the species is ovo- 

 viviparous or oviparous. 



If a study of specimens of Pseudococcus can be made with 

 the insects in a natural condition, the manner of oviposition is a 

 good specific character. Whether a species is ovoviviparous or 

 oviparous is not always a sharply separated condition, for an 

 individual may give birth to living young and also deposit 

 eggs. However, the formation of an egg sac is an indication 

 that a species is oviparous and the formation of this egg-sac is 

 constant for the species. In a normally ovoviviparous form a 

 mealy secretion which is distinctly of a fibrous nature is made 

 upon the plant. Crawii Coq. and longispinus Targ. do not 

 form a distinct egg-sac but form a mealy secretion upon the 

 plant. Citri Risso and obscurus Essig form an egg-sac of con- 

 siderable size. Agrifoliae Essig forms an egg-sac but not so 

 extensive a one as the last two named species. 



The writer is working on a monograph of the North Amer- 

 ican species of this genus. He would be glad to exchange 

 specimens of Coccidae for species of Pseudococcus not now in 

 his collection. Correspondence to this end is invited. 



