No. 555] SPECIES-FORMING OF ECTO-PARASITES 143 



occur on the European curlew, Numenius arquata, of 

 which one occurs also on the new world curlew, Numen- 

 ius longirostris. It is the only Mallophagan so far re- 

 corded from this host. Hcematopus galapagoensis, limited 

 to the Galapagos Islands, has three Mallophagan species, 

 of which one is peculiar to it, one is a duck-infesting spe- 

 cies, probably a normal straggler under conditions which 

 I shall explain later, and one is a form found also on 

 Hcematopus ostralegus, the common oyster-catcher of 

 Europe, Central Asia and Africa. The old world avocet, 

 Recurvirostra avocetta, has six Mallophagan species, 

 while the new world avocet, Recurvirostra americana, has 

 four, of which two, Nirmus pileus and Nirmus signatus, 

 are common to both hosts. The other two are new. Two 

 species of the curious aberrant Charadriiform family 

 Parridae occur in the host-list, each having but a single 

 Mallophagan species, and that the same for both hosts. 

 One of the host species is limited to Australia, while the 

 other ranges from India to the Malay Peninsula. 



The Gruiformes, or cranes, thirty-four living species, 

 are represented in the host-list by twelve species, para- 

 sitized by twenty Mallophagan kinds. The herons and 

 egrets, order Ardeiformes, are represented by forty-five 

 species. Lipeurus leucopygus occurs on both the old 

 world bittern, Botaurus stellaris, and the new world one, 

 Botaurus lentiginosus. It occurs also on two other 

 herons, both old world species. From Butorides sunde- 

 valli, peculiar to the Galapagos Islands, I have had four 

 species, all previously described by me from various mar- 

 itime birds of the Pacific. This is a case of straggling, 

 but as I shall point out later in connection with the condi- 

 tions shown by certain other Galapagos Island hosts, 

 a case of what may be called normal straggling, unusual 

 on the whole, but possible and especially common in the 

 case of Galapagos, and perhaps other, island hosts. 



The Palamedeiformes, or South American screamers, 

 are represented in the host-list by two species, parasi- 

 tized by three Mallophagan kinds. One of these is com- 



