9 8 



Geese of Europe and Asia 



shorter, but at the same time also broader and more rounded both longitudinally and 

 transversely. This difference in the form of the bill and nail is clearly shown in Plate 23 of 

 the present work. In addition, I give figures of the bills, taken from above, of both 

 M. arvensis and M. segehtm, by comparison of which the essential difference in the size of 

 the upper nail will be very apparent. 



We may first of all notice that, as shown by the dotted lines across these figures, in 

 M. arvensis the length of the nail is included in the total length of the bill usually 

 considerably more than 4 times, or, far less frequently, 4 times, while in M. segetum the nail is 

 included in the total length of the bill considerably less than 4 times, or not more than 31 

 times, so far as I can judge from the examples of the latter species I have had in my hands. 



M. segetum, $ 

 Culmen 60I mm. 

 (Northern Russia.) 



M. arvensis, $ 

 Culmen 66 mm. 

 (St. Petersburg.) 



M. arvensis, 9 



Culmen 70 mm. 



(Ryazan.) 



These differences in the structure and form of the bills of the yellow-billed and the 

 bean- goose were long since clearly and intelligibly described, as well as figured (although 

 the figures were, in my opinion, inaccurate), by Mr. Naumann, 1 but unfortunately attracted 

 scant attention among ornithologists, who concluded that as a guide to the discrimination 

 of these two species it sufficed to confine themselves to the distribution of the black and 

 orange areas on the bills, in consequence of which, as we shall see farther on, they could not 

 avoid coming to the erroneous deduction (not having understood the gist of what Naumann 

 had told them) that these two geese constitute but one species with a bill very unstable both 

 in shape and colouring. 



To return to the bill of M. arvensis, we find behind the nail, towards the nares, that 

 it is very flat above, but farther towards the base becomes gradually stouter, and is fairly 

 high and wide at the forehead. The feathering of the forehead extends on to the base of 

 the bill in a fairly regular flat arch. The feathering at the sides of the upper mandible 

 also projects into this in regular semicircles, whence it results that the naked angles 

 of the bill, projecting into the feathering at the sides of the forehead, are considerably 

 farther removed from the tip of the nail than is the extreme point of the feathering in the 

 upper angle of the gape. 



1 Naumannia, 1853, taf. 7. 



