NATURAL SCIENCES OF PniLADELrHIA. 535 



eiices for tlie use of students who have paid less attention than myself to the 

 subject.* 



In concluding, I desire to express my thanks to several members of the 

 Academy of Natural Sciences who have assisted and encouraged me, and es- 

 pecially to Dr. Jos. Leidy. 



A Review of the TERNS of North America. 

 BY ELLIOTT COUES. 



s'^.UA^ 



Considerable difiference has prevailed among ornithological writers with re- 

 gard to the relationships of many of the North American SterinniK with the 

 representative species of Europe. Having at command a very extensive series 

 of specimens from both continents, I have instituted a careful comparison of 

 the more or less intimately related species, believing that the results of 

 such an investigation would not prove unacceptable to ornithologists. While 

 this has been the principal aim of the present paper, I have endeavored to pre- 

 sent fairly the data tending to determine some other points of synonymy and 

 relationship which even at this late day remain open to discussion ; and to 

 give such stages of plumage as are not already too well known to require no- 

 tice. The paper is not to be considered in any sense as a monograph ; I have 

 endeavored to express its character in its title. 



I am under particular obligations to Mr. G. N. Lawrence and Mr. D. G. El- 

 liot, for the opportunity of examining several unique and typical specimens, 

 and unusual stages of plumage, of wliich the museum of the Smithsonian In- 

 stitution does not contain examples. 



Family LARID^. 



Subfamily STERNIN^. 



Section STERNEJi]. 



Genus GELOCHELIDON Brehm. 



Gelochelidon, Brehm, Vog. Deutsch. 1830. Type S. anglica, Mont. 

 Laropis^ Wagler, Isis, 1832, p. 1225. Same type. 



Char. — Bill shorter than the head, extremely robust, not very acute; its 

 height at base nearly a third of its total length along culmen ; prominence at 

 symphysis well marked, but not very acute, situated so far back as to make 

 the gonys equal in length to the rami, reckoning from the termination of the 

 feathers on the side of the mandible. Culmen very convex ; gonys straight ; 

 commissure gently curved. Wings exceedingly long, and acute ; each feather 

 a full inch longer than the next. Tail rather short, contained 2^ times in the 

 wing; in form deeply emarginate, but its lateral feathers without the elonga- 

 tion oi Sterna. Feet long and stout; tarsus a little shorter than the bill, ex- 

 ceeding the middle toe and claw. Hind toe well developed; inner shorter 



* Several authors not mentioned in our former work may here be briefly cited. 



Borellus, De Motu Animalium. 



Camper, Beobachtiiugen der Berlinischcn Gesellsf haft, vol. i. 1787. 



Von dem Fluge der \ oegel, Sthriften der Berlinischen Gesellscbaft, vol. ii. 1781, p. 214. 



Mayer, Das aufrecht Stehen. Mueller's Arohiv, vol. xx. 1853, p. 9. 



Fick, Ueber die Gestaltung der Gelenkflaechen. Mueller's Arcbiv, 1853, vol.xx. p. 657. 



Schuebler, Bedeutung der .Mathematik fuer die Naturgeschichte. Jahresbelte des Vereins fuer 

 Vaterlandskunde, Stuttgart, 1849. 



Dr. J. Aiken Meigs, Kelation of Atomic Heat to Crystalline Form, vol. iii. Jour. Acad. Nat. Sc . 

 Philadelphia, 1855-58, p. 105. 



Prof Popoff, Description de la Courbc fruiforme. Bulletin de la Societe des Naturalistes de 

 Moscou, 1859, part i. p. 283. 



Zeising, Ueber die Metamorphosen in den Verhaeltnissen der menschlichen Gestalt. Acta 

 Academic Cesareas Leopoldino-Carolinae, vol. xxvii. part ii. 



1862.] 



^i 



