No. 555] SPFCIFS-FOFMFXG OF ECTO-PABASITES 151 



from forty new world host kinds, including several 

 genera and species peculiar to the Galapagos Islands. 

 All the specimens from Galapagos Island hosts show a 

 number of small but obvious distinguishing characters, 

 and I have given them the varietal name galapagoensis. 

 This constant distinction would indicate that the Gala- 

 pagos individuals, though now infesting several different 

 host kinds, are all descended from a single original intro- 

 duction of the species; or that there is some external 

 modifying condition of life on Galapagos Island birds 

 that would produce a convergence among the descendants 

 of ancestors representing several introductions, a sup- 

 position hardly tenable, especially in the light of the pe- 

 culiar life conditions of the Mallophaga. 



The Passeriform family Tyrannidse, the new world 

 flycatchers, is represented in the list by eighteen species 

 parasitized by two Mallophagan species, of which but 

 two, one being Docophorus communis, are recorded from 

 old world Passeriform hosts. Although this family has 

 a continuous geographical distribution over North, Cen- 

 tral and South America, there is no unusual commonness 

 of parasitic distribution in it. No one Mallophagan kind 

 occurs on more than two flycatcher species, except in the 

 Galapagos islands, where Nirmus vulgatus var. gala- 

 pagoensis is found on all three of the flycatcher kinds 

 occurring there. All the other Mallophagan species on 

 these Galapagos flycatchers are forms restricted to the 

 islands, although not to the flycatchers. 



The swallows, Hirundinidae, are represented by ten 

 species of which two are old world, five new world, two 

 both old and new world, and one from the Galapagos 

 Islands. From them are recorded twenty Mallophagan 

 species, of which Menopon rusticum is found on one old 

 world, one new world, one old and new world, and one 

 Galapagos Island host. Docophorus excisus is found on 

 one old world and two new world hosts, and Nirmus 

 lohgus on two new world and the two old and new world 

 boats. Seven Mallophagan species have been taken from 



