1911] Specific Characters in Pseudococcus 319 



character very variable. Kellogg & Smith, '04, found that in 

 twenty-five specimens of Cereputo yuccae, a closely allied 

 genus, no two formulae agreed, "and that there was practically 

 as much variety in these formulae as there is among the eleven 

 formulae published as specifically diagnostic for eleven North 

 American species of the genera Cereputo and Phenacoccus." 

 Again Tinsley, J. D., 'OS, in discussing the variation in the 

 antennae of P. virgatus Ckll. gives eleven different formulae. 

 Again the same author, 1900, in his description of a new species, 

 P. texensis Tins., gives three different formulae. Ehrhorn, 

 Edw. M., 1900, in his description of a new species, P. maritimus 

 Ehr., gives four formulae. The universal use of antennal for- 

 mulae in descriptions is unfortunate, as this has given an excuse 

 for the creation of new species and is valueless in analytical 

 tables for the determination of specimens. The sooner that 

 the valuelessness of this character is realized by systematists 

 describing new species of this genus, the sooner will a search for 

 valuable characters be begun and a serious mistake in taxonomy 

 be corrected. 



Legs. Tables 11-15. The length of the legs is used to 

 quite an extent in descriptions. Their length compared to the 

 length of the antennae is often stated, also the length of the 

 different segments compared with each other. They are often 

 spoken of as long and strong. The presence of hairs is often 

 noted, also that of knobbed digitules. 



For the study of the legs five specimens of each species were 

 used. They were the same specimens that were used in the 

 study of the antennae. The measurements of the different 

 segments are the greatest length of these segments, so that the 

 sum of the lengths of the different segments will be greater than 

 the length of the leg. Like the basal segment of the antennae, 

 the coxa is very difficult to measure and the results are not 

 entirely reliable. 



At the right hand side of the tables, formulae are 

 appended. These formulae are constructed in the same man- 

 ner as the antennal formulae. The segments are numbered in 

 order beginning with the coxa. 



The formulae show but little if any more satisfactory results 

 for specific determination than do the formulae of the antennae. 

 The formulae of each pair of legs for each of the species will be 

 discussed together. 



