NATURAL SCIENCES OF PHILADELPHIA. 
535 
ences for the 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. 
Considerable difference has prevailed among ornithological writers with re- 
gard to the relationships of many of the North American Sterninse 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 which the museum of the Smithsonian In- 
stitution does not contain examples. 
Family LARIDJE. 
Subfamily STEBNINiE. 
Section ST ERNE M. 
Genus GELOCHELIDON Brehm. 
Gelochelidon, Brehm, Yog. 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 culrnen ; 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. Culrnen 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 2J times in the 
wing ; in form deeply emarginate, but its lateral feathers without the elonga- 
tion of 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 Animal ium. 
Camper, Beobachtun gen der Berlinischen Gesellschaft, vol. i. 1787. 
Von dem Fluge der Voegel, Sehriften der Berlinischen Gesellschaft, vol. ii. 1781, p. 214. 
Mayer, Das aufrecht Stehen. Mueller’s Archiv, vol. xx. 1853, p.9. 
Fick, Ueber die Gestaltung der Gelenkflaechen. Mueller’s Archiv, 1853, vol.xx. p. 657. 
Schuebler, Bedeutung der Mathematik fuer die Naturgeschichte. Jahreshefte des Vereins fuer 
Yaterlandskunde, Stuttgart, 1849. 
Dr. J. Aiken Meigs, Relation of Atomic Heat to Crystalline Form, vol. iii. Jour. Acad. Nat. Sc . 
Philadelphia, 1855-58, p. 105. 
Prof. Popoif, Description de la Courbe 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 
Academiae Cesar ere Leopoldino-Carolinte, vol. xxvii. part ii. 
1862 .] 
