536 PROCEEDINGS OF THE ACADEMY OP 



than outer; interdigital membranes deeply incised, especially the inner. Tail 

 and rump concolor with tbe back. Size moderate. 



Gelocheliflon is a well-marked generic form of the Slerninie, 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 Sterme. It differs in coloration above from most of the other genera 

 of Tei'ns, in having the pearl blue mantle continued over the rump and tail. 



The name Gelochdidon was proposed by Brehm two years before Wagler 

 instituted his genus Laropis. Both are founded upon the same type, — S. an- 

 glica, Mont. 



Gelochklidon axglica Bp. ex Mont. 



Sterna anglica, Montagu, and of authors. 



TJvilasseus anglicus, Boie, Isis, 1822, p. 563. 



Laropis anylica, Wagler, Isis, 1832, p. 1225. 



Gelochdidon anglica, Bp. Comp. List, 1838, p. 61. 



Gelochelidon palustris, Macgill., Man. Orn., 1842, ii. p. 237. 



Sterna aranca. Wilson, Am. Orn. Lawrence, Gen. Rep., 1858, p. 859. 



Gelochelidon aranea, Bonap., Comp. List, 1838, p. 61. 



DiAG. — Sterna rostro breve, robustissimo, nigro ; dorso cEerulescente-perlaceo, 

 uropygio caudaque concoloribus ; remigibus primariis argentato-griseis, vis 

 albo intus marginatis, nisi basin versus; corpore subtus albo, pedibus nigris. 



Habitat. — Atlantic Coast of America, from Massachusetts southward. Europe. 



This species differs from all the other Terns of North America, except Sterna 

 antiUarum, 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 sufBcient 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 ditference exists. 

 I have minutely compared the specimens before me, and found them absolutely 

 identical in every particular of size, form and color. 



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 1 838, — 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, Isis, 1822, 563. Type S. caspia, Pall. 



Hydroprogne, Kaup, Sk. Ent. Eur. Thierw., 1829, 71. Same type. 



Sylochelidon, Brehm, Vug. Deutsch. 1830. Same type. 



Helopus, Wagler, Isis, 1832, 1224. Same type. 



Actochclidon, Kaup, Sk. Ent. Eur. Thierw., 1829, 31. Type S. cantiaca, Gra. 



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 emurginate ; in other species more 



[Dec. 



