110 Mr. 0. Salvin on the Genus Cinclus. 



look. At the same time it must ever be borne iu mind that a 

 certain amount of individual variation exists in all species, and 

 that the history of every one is distinct from that of every other. 



Taking this view, it follows that, instead of species having 

 one minimum standard of value which would exclude constant 

 forms of slight difference, the standard must be lowered to 

 the point where constancy of differential character begins, thus 

 taking a closer view of the varied degrees of the relationship 

 which exists between species. 



The genus Cinclus may well be made to illustrate the dif- 

 ferent degrees of affinity which subsist between the component 

 specieso f many genera. Thus the relations of C. aquaticus to 

 C melanogaster, of the same to C. leucogaster, of the same to C. 

 pallasi, and of the same to C leucocephalus are all of markedly dif- 

 ferent values ; and I have endeavoured, after assigning a name to 

 every constant form, to show in the subjoined list the degree of 

 difference each possesses. To do so, I have used the term " local 

 race'' for slightly modified forms inhabiting separate but com- 

 paratively adjacent districts, and that of " representative species'' 

 where the affinity is still clearly shown, but the difference 

 more decidedly marked. I have not yet noticed the co-ex- 

 istence of closely allied forms in the same area in this genus; 

 but the range of C. melanogaster doubtles^ sometimes overlaps 

 that of C. aquaticus in the winter months, the return of the 

 former to its own ground in summer restoring the separation of 

 the two races in the breeding- season. 



The distribution of Cinclus extends over the whole Palaearctic 

 region where suitable mountain-streams occur. In the Indian 

 region it is confined to the Western Himalaya and the island of 

 Formosa. It also extends throughout the Rocky Mountains of 

 the Nearctic region, and continues thence along the same chain 

 into Southern Mexico, Guatemala, and Veragua, the northern pro- 

 vince of the Neotropical region. In the Neotropical region it is 

 again found along the streams of the Andes, from New Granada 

 to Bolivia. No species are recorded from any portion of either 

 the Ethiopian or Australian region. 



The following is a list of the species of Cinclus, geogra- 

 phically considered : — 



