POLISH SWAN. 



229 



Height, from the base of the under jaw to the vertex of 

 the head, just behind the orbit of the eye, in C. immu- 

 tabilis, two inches and one-eighth ; C. olor, two inches and 

 one-quarter. In C. immutabilis the bill is rather more 

 flattened, particularly in the middle, between the dertrum, 

 or nail, and the nostrils ; the protuberance at the base of 

 the upper mandible is less developed. In the Polish Swan 

 the cranium is highest at the supra-occipital portion ; in 

 the Mute Swan the cranium is highest at the supra-orbital 

 portion ; but the greatest difference is perceptible on com- 

 paring the occipital bones ; the upper portion of this bone 

 in C. immutabilis protrudes considerably more, and there 

 are two oval foramina, one on each side just above the 

 foramen magnum, which are not present in any specimens 

 of C. olor that I have examined ; the portion forming the 

 boundary of the external orifice of the ear is much more 

 prominent, and the condyle forms a more acute angle with 

 the basilar portion of the occipital bone. 



I have verified all Mr. Pelerines observations. 



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