218 OK THE SPECIFIC DISTINCTION OF THE BRIDLED GUILLEMOT. 



distinctions, and that although allied species may possibly at times exhibit 

 the like, as variations from the usual type, — perhaps even exhibit them in 

 these exceptional instances more decisively marked. I allude, with reference 

 to the species before us, to the particulars of size and colour, the common 

 species, Zfria troile, being by some said to be, if anything, rather larger 

 and rather darker, while by others the TJria laehrymans is so described, 

 and the bill rather stouter. This last, though perhaps not a common 

 variation, is certainly a mere variation, as in the instance of the Crossbill, 

 and perhaps in the Nutcracker. And so also with regard to size; the fact 

 is, there are found larger and smaller and heavier and lighter birds in each 

 case. In addition, however, to these there is another, which may be called 

 an "ocular demonstration" of the specific difference between the two species. 

 The eye in this Guillemot, (TJria laehrymans,) has been noticed by John 

 Gatcombe, Esq., of Wyndham Place, Plymouth, a very exact and accurate 

 ornithologist, and described in a letter to me, as being considerably larger 

 than in the other. It is encircled by a narrow white band or rim, from 

 which the white line extends backwards and downwards about an inch and 

 a half. This line, from which the bird derives its name, in the Latin, 

 French, and English languages, is the chief apparent mark of difference, 

 the main feature on which its specific distinction has been contended for. 

 It has never, I believe, been imagined to be a characteristic of either sex 

 of the common species, but, on the contrary, is seen in the male as well 

 as the female, in both old and young birds, and that in spring, summer, 

 autumn, and winter. 



The question then is, is this a real specific distinction, or is it merely an 

 occasional though perpotually recurring variety, a variety whose range would 

 appear to be defined, the chief station of the bird bearing it being Spitz- 

 bergen; while as ragards the British coasts, individuals have occurred in 

 every or almost every place where the TJria troile is commonly seen. 



Now with regard to colour, it will, I believe, be found that, as already 

 mentioned, this species is specifically darker, that is, in old and mature 

 specimens, than Uria troile. Old birds of the latter species would 

 seem to become lighter than the young ones; while with the present species, 

 so to call it, the case is reversed, old birds becoming almost black. 



Again, the white circle round the eye, and the line of extension from 

 it, has nothing to do with age, for, as remarked in a letter to me from 

 Mr. Gatcombe, the white line is quite distinct in a young bird of the year, 

 in its first winter plumage. Now, in the first place, I do not think that 

 in the case of birds, varieties occur in perpetuity with such exactitude as 

 in the present case, or as they certainly do in insects. Prima facie, if 

 the mark at the back of the head may be so spoken of, it is naturally 

 to be judged that the -two birds, the one with it, the other without it, 



