o38 PROCEEDINGS OF THE ACADEMY OF 



Habitat. — In America, the interior of the Fur Countries; Hudson's Bay; 

 Labrador; in winter ranging southward along the Atlantic Coast as far as New 

 Jersey. 



This species in all its stages of plumage is too well known to require any 

 further description. 



Quite a large series of American skins, of all ages, compared with two fully 

 adult birds from Europe, constantly differ in size and proportion, as shown by 

 the following measurements: 



Comparative measurements of American and European Birds. 



American. European. 



Length of bill along culmen 2-75* 2-40 



" " " gape 4-00 3-a5 



Height " at base 0-90 0-75 



"Width " opposite nostrils 0-50 0-50 



Length of wing from flexure 16-50 15-00 



" " tarsus 1-75 1-65 



" " middle toe and claw 1-65 1-55 



" " tail 5 75 5-25 



The above measurements indicate the average of the specimens from both 

 countries before me, from which it will be seen that the American bird is de- 

 cidedly the larger. While the bill is nearly a third of an inch longer, it is also 

 especially remarkable for its great comparative height at the base, and its width 

 at base being no greater than in the European bird, gives it quite a different 

 shape. The next most patent difference lies in the lengtli of wing from the 

 flexure, in which the American bird surpasses the European by fully Ij- inches. 

 Specimens of both, of course, differ among tuemselves to a degree; but the 

 greatest variation in adult American skins is hardly half an inch. The wing 

 of the adult European bird, indeed, hard'y equals that of a young bird of the 

 j'ear from America ; and it is well known how much smaller are the young of 

 all Terns than the adults. The tarsi and toes of the two, as well as the tail, 

 differ in a considerable degree, but not so markedly as do the bill and wings. 

 I find no differences whatever in the color of the two birds. 



With but two specimens of the European bird before me, I do not venture to 

 formally separate from it its North American representative. But should these 

 examples prove to represent fairly the characters of the European bird, and the 

 discrepancies in size and proportion above pointed out prove constant, I should 

 not hesitate to do so. In that event I would propose for our bird — in the ab- 

 sence of any very peculiar characters on whicii to base a name, and in view of 

 the fact that it is the largest and most magnificent Tern of our continent — the 

 name of Thalasseus imperator. 



The following would be its diagnosis : 



Til. Tlialassco cafpio coloribus similis ; sed omnino major, rostro etiam vali- 

 diore, lorgiore, aliiore nee latiore. Rostr. long. 2-75 poll.; ala; 1650. 



The proper specific appellation of the Caspian Tern is not '^caspia Pallas," 

 but " tschegrava Lepechin," which latter name 's proposed in the same work in 

 ■which Pallas calls the bird '' ca.s7)/«," but has priority by several pages. As, 

 however, the word is not only barbarous, but also exceedingly cacophonous, 

 and especially as caspia has become so well established by common consent, I 

 do not think it would be expedient to supersede Pallas' name, in view of the 

 very slight priority of that of Lepechin. 



Thalasseus eegius Gambel. 



Sterna cayana, Bon., 1828 ; Nutt., 1834; Aud., 1839 and 1844; but not of 

 Latham. 



* Inches anil hundredths. 



[Dec. 



