Letters, Extracts from Correspondence, Notices, fyc. 231 
M. Bolle rests his arguments in favour of establishing a new 
species, firstly, on some supposed peculiarity of colour. After 
having given a description of his bird, he adds, u II reste h remar- 
quer qu’autant que je me rappelle [the italics are mine], il n’offre 
point de grandes variations suivant la saison ou suivant le sexe, 
et qu’en aucun temps il ne presente la plus legere trace de vert.” 
Now this is rather indefinite language for any one attempting 
to establish a distinct species—a matter in which the conscience 
of an ornithologist should be particularly tender, when it is 
considered what confusion has been induced by a too great 
readiness in authors to stand sponsors to species which could 
readily dispense with their well-meant offices. 
As an illustration, I might take the Columba trocaz, which is 
described by Dr. Heineken in f Brewster’s Journal 9 as a new 
species, though it is doubtless identical with the Columba lauri- 
vora of Webb and Berthelot. Montagu fell into a like error in 
the case of his Alauda trivialis, which is no more than our old 
friend the Anthus pratensis after its autumnal moult, 
M. Bolle does not enter into any particular description of the 
young bird of the year of his assumed species, nor does he tell 
us whether he has noted at what season of the year his speci¬ 
mens were obtained. All he tells us is that he has made a 
careful examination of several skins which he brought from the 
Canary Islands, and instituted a comparison, which he says had 
hitherto been neglected, between these skins and those of the 
true Pipit. 
Secondly, M. Bolle urges that the size of his bird is smaller 
than that of the A . pratensis, and that the relative length of the 
claw in his specimen is greater. 
I am quite aware of the difficulty of giving accurate descrip¬ 
tions of birds, and of the danger of trusting too implicitly to 
measurements if you have only prepared skins to rely upon; 
for, in spite of the greatest care, colours will fade, and skins will 
shrink, if, indeed, they have not been stretched or displaced in 
the process of preparing them. This led to my taking very 
accurate descriptions and measurements of birds in the flesh, in 
Madeira, in the year 1851. I append a description thus taken 
of the A. pratensis. In the summer of the same year I brought 
