NEW MALLOPHAGA. 543 



related to Old World hosts, are presented by Docophorus 

 communis and Nirmus fuscus. These two parasite species 

 are found, common, in one case, to many passerine birds, 

 and in the other, to several raptorial birds, which differ 

 generically from the Old World hosts. It will be noted, 

 however, that both of these species have a wide range of 

 hosts in both Europe and America. The fact is that we 

 have to do here, in each case, with a group of closely 

 allied, insensibly gradating forms, rather than with a single 

 well marked Mallophagous species. That this condition 

 has been recognized by the European authors is shown 

 in the cases of both Docophorus communis and Nirmus 

 fuscus, by the attempts which have been made by Giebel 

 and Piaget to break up these species into several distinct 

 species (Giebel), or into subspecies (Piaget). 



Finally with regard to the constant or occasional ap- 

 pearance of the parasites on the hosts, I can add also but 

 little. In the preparation of this paper I have had no 

 such long series of specimens of one bird species as it 

 was my privilege to have of certain species of maritime 

 birds. As an illustration of the varying degrees of pre- 

 valence of different parasite species infesting a single 

 bird species, the parasites of Carpodacus mexicanus 

 frontalis, the House Finch, may be referred to. Of nine 

 specimens of this bird species examined, six were infested 

 by Docophorus communis, four by Nirmus vulgatus, and 

 one by Physostomum microcephalism. Of three specimens 

 examined of the closely related Carpodacus purpureus 

 calif 'ornicus, the California Purple Finch, Docophorus 

 communis was found on each, but no Nirmus nor Phy- 

 sostomum on any. Physostomum as a parasite, however, 

 is not always uncommon on its host, as the case of Phy- 

 sostomum diffusum, found on five out out of seven speci 

 mens of Melospiza fasciata samuelis, attests. 



