Art. 19 LICE OF THE GENUS PEDICULTJS EWING 6 



be added ihat corporis De Geer (1778) has priority over vestimenti 

 Nitzsch (1818), a name which is also frequently applied to the 

 clothes louse. 



When in 1778 De Geer gave the varietal name capitis to the head 

 louse and corporis to the body or clothes louse he did not employ 

 the specific name, repeated as a varietal name, to represent either 

 of his varieties — which is required according to modern usage — 

 hence there has been some question as to which varietal name of De 

 Geer should be dropped. 



It appears to the writer that the name humanus (either varietal 

 or specific) of Linnaeus should be applied to the head louse for two 

 reasons. In the first place it was the variety first described by De 

 Geer in 1778. In the second place, it is the head louse that has long 

 been considered as the genotype of Pediculus where the two forms 

 have been regarded as distinct species. 



The whole matter is somewhat involved and apparently is not 

 sufficiently covered by our entomological codes of nomenclature or 

 by the International Code of Zoological Nomenclature. 



CHARACTERS OF TAXONOMIC VALUE IN THE GENUS PEDICULUS 



The characters which have been most used in the past for taxo- 

 nomic purposes have had to do largely with size, degree of chitiniza- 

 tion, ratio of lengths of antennal segments, and chaetotaxy. Un- 

 doubtedly such characters have much taxonomic value, but the range 

 of individual variation and the possible effects of hybridization 

 should be taken into consideration at all times. 



Mjoberg (1910) used the shape of the genital plate of the female 

 and the form of the gonopods in differentiating his P. afflnis from P. 

 consohrinus Piaget. Fahrenholz (1917) used a large number of char- 

 acters including size, pigmentation, chaetotaxy, shape of gonopods, 

 shape of antennal segments, etc. Nuttall (1920) pointed out and, 

 according to the view of the present writer, demonstrated that size 

 is such a variable character that its use in taxonomic differentiation 

 should be with much reservation and caution; also, he demonstrated 

 that coloration was so variable a character as to be wholly unreliable 

 for taxonomic purposes. He showed that not only was there great 

 variation between individuals in regard to pigmentation but also 

 that the degree of pigmentation was dependent chiefly on environ- 

 ment, and he further showed that in a single individual certain parts 

 would vary in their pigmentation in a more or less indiscriminate 

 manner. Among the characters that Nuttall (1920) found to be 

 of value are : The shape of the head, the length of the antennae, and 

 the shape of the sixth abdominal segment. 



In the course of the writer's study it was found that in specimens 

 properly cleared and mounted the pleural plates offered characters 



