ARCTIC BLUE-THROATED ROBIN. 275 
I found this species by no means uncommon in the swampy districts 
near Valkenswaard, in Holland. 
The only difference between this and the preceding species is in the 
colour of the throat-spot, which is pure white. There are three forms of 
the Blue-throated Robin, the adult males of which, when in full breeding- 
plumage, may be readily distinguished. First, we have the Northern or 
Arctic form, with the spot in the centre of the throat red; secondly, the 
South-European form, with the spot in the centre of the throat pure and 
silky white; and thirdly, the form of which the throat is uniform blue. 
The two former of these birds have different breeding-grounds, and quite 
distinct areas of geographical distribution ; but the uniform-blue-throated 
form is chiefly met with in localities frequented by the Southern or white- 
spotted form. In the specimens I have examined of this blue-throated 
form, in which the breast at first sight appeared unspotted blue, I have 
generally found the bases of the feathers on the throat white. Newton, 
in his edition of Yarrell’s ‘ British Birds, asserts that these differ- 
ences of plumage (especially in the white-spotted and spotless forms) are 
coexistent with differences in the length of the tarsus; but in an examina- 
tion of a series of these birds, I find that the measurement of the tarsus is a 
variable quantity, and of no value in separating the species. 
