536 
PROCEEDINGS OF THE ACADEMY OP 
than outer ; interdigital membranes deeply incised, especially the inner. Tail 
and rump concolor with the back. Size moderate. 
Gelochdidon is a well-marked generic form of the Sterninse , embracing several 
species agreeing in their short, very robust bills, exceedingly long wings, length- 
ened tarsi, and short tail, — which latter never attains the deeply-forked shape 
of typical Sterns, s. It differs in coloration above from most of the other genera 
of Terns, in having the pearl blue mantle continued over the rump and tail. 
The name Gelochelidon was proposed by Brehm two years before Wagler 
instituted his genus Laropis. Both are founded upon the same type, — S. an - 
glica, Mont. 
Gelochelidon anglica Bp. ex Mont. 
Sterna anglica , Montagu, and of authors. 
Thalasseus anglicus , Boie, Isis, 1822, p. 563. 
Laropis anglica , Wagler, Isis, 1832, p. 1225. 
Gelochelidon anglica , Bp. Comp. List, 1838, p. 61. 
Gelochelidon palustris, Macgill., Man. Orn., 1842, ii. p. 237. 
Sterna aran%a. Wilson, Am. Ora. Lawrence, Gen. Rep., 1858, p. 859. 
Gelochelidon aranea, Bonap., Comp. List, 1838, p. 61. 
Diag. — Sterna rostro breve, robustissimo, nigro ; dorso caerulescente-perlaceo, 
uropygio caudaque concoloribus ; remigibus primariis argentato-griseis, vix 
albo intus marginatis, nisi basin versus ; corpore subtus albo 3 pedibus nigris. 
Habitat . — Atlantic Coast of America, from Massachusetts southward. Europe. 
This species differs from all the other Terns of North America, except Sterna 
antillarum , in having the rump and tail of the same color with the back. Its 
primaries differ from other species — though approaching nearest to Thalasseus 
caspius — in having the inner webs white for a comparatively short space; and 
the white is not pure, nor is there a very trenchant line of division between it 
and the dark portions of the feathers. , 
I have not a sufficient number of skins before me for a perfectly satisfactory 
comparison of the birds of the two continents, but, so far as I can judge, I am 
decidedly inclined to agree with Audubon in opinion, that no difference exists. 
I have minutely compared the specimens before me, and found them absolutely 
identical in every particular of size, form and color. y v ' ’ ' 
The American bird was first described by Wilson, under the name of Sterna 
aranea , that author, perhaps, considering it distinct from, but much more pro- 
bably being unaware of the existence of, the European bird. It was very 
properly referred by subsequent American writers, — Nuttall, Audubon, and Bona- 
parte up to 1838, — to the latter. At that date, in his Comparative List, Bonaparte 
distinguishes it from the European bird under the name of Gelochelidon aranea , 
and his example has been generally followed by writers since that time. 
Genus THALASSEUS Boie. 
Thalasseus , Boie, Isi3, 1822, 563. Type S. caspia , Pall. 
Hydroprogne , Kaup, Sk. Ent. Eur. Thierw., 1829, 71. Same type. 
Sylochelidon , Brehm, Vog. Deutsch. 1830. Same type. 
Helopus , Wagler, Isis, 1832, 1224. Same type. 
Actochelidon , Kaup, Sk. Ent. Eur. Thierw., 1829, 31. Type S. cantiaca, Gin. 
CH.---Size very large, large, or moderate; general form more or less robust; 
a decided occipital crest. Bill as long as, or longer than, the head, robust, 
height at base a third to a fourth the length of culmen. Culmen variable in 
amount of curvature; position of the angle at symphysis variable. Wings 
moderately long (for this subfamily); pointed and acute ; but the first primary 
not surpassing the second by as much as the latter surpasses the third. Tail 
moderate or short; in the type of the genus very short, being contained three 
times in the wing, and but moderately emarginate; in other species more 
[Dec. 
