NATURAL SCIENCES OF PHILADELPHIA. 129 



not subject to any great variations with age, sex, or season. Species, B. skua 

 (type) and B. antarcticus. 



Stercorarius. Bill equal to middle toe without the claw, moderately robust, 

 height at base more than a third of culmen ; striae and sulci fewer and more 

 slightly marked. Encroachment of feathers on bill very great, especially on 

 the upper mandible, where it greatly exceeds that on the lower, and is of a 

 different outline from that of Buphagus. Occiput decidedly subcrested. Wings 

 exceedingly long, the primaries narrow, tapering, with quite acute tips. Tail 

 long ; the lateral feathers more or less graduated ; the central pair considera- 

 bly, sometimes excessively, elongated, tapering and filamentous. Feet rather 

 slender, the tarsi equal to, or slightly longer than the middle toe and claw. 

 Size moderate or small. Form less robust, general organization much less 

 powerful. Nearly bicolor when adult ; passing through very various states 

 of plumage before arriving at maturity. Species, S. pomarinus, parasiticus, 

 (type) Richardsoni, Hardi/i, spinicauda, Buffoni. 



Of these, the five last are very strictly congeneric in every particular. 

 Pomarinus, by its larger size, somewhat more powerful form, shorter and 

 broader central tail feathers, &c, shows a slight aberration towards Buphagus. 

 But in all other features the essential characters of Stercorarius are so strongly 

 pronounced, that it cannot afford a link by which the two genera may be 

 united. 



? Stercorarics pomarinus Vieill. ex Temm. 



Larus parasiticus, Meyer et Wolf, Tasch. Deutsch. ii. 1810, 490. (Sed non 



Linn, nee auct.) 

 Larus crepidatus, Gmelin, Systema Naturae, i. 1788, 602. Latham, Index Or- 



nithologicus, 1790, ii. 819. (Citat Sterc. striatum, Briss.) 

 Stercorarius striatus, Brisson, Ornith. vi. 1760, 152, pi. 13, fig. 2. (Juvenis.) 

 Lestris striatus, Eyton, British Birds, 18 , 53. 

 Lestris pomarinus, Temminck, Man. Orn. ii. 1820, 793. Temminck, Man. 



Orn. iv. 1840, 495. Faber, Prodromus Island. Ornith. 1822, 104. 



Brehm, Naturg. Europ. Vogel, 1823, 741. Bonaparte, Synopsis, 1826, 



No. 305. Lesson, Manuel Ornith. 1828, ii. 388. Kaup, Sk. Ent. Europ. 



Theirw. 1829, 64. Swainson et Richardson, F. B. A. 1831, ii. 429. 



Nuttall, Manual Ornith. ii. 1834, 315. Audubon, Ornith. Biograph. 



1839, hi. p. 396. Audubon, Synopsis, 1839, 332. Audubon, Birds 



America, 1844, vii. 186, pi. 451. Keyserling et Blasius, Wirbelth. 



Europ. 1840, i. 240. Schinz, Europ. Fauna, 1840, i. 388. Schlegel, 



Rev. Crit. Ois. Europ. 1844, 84. Bonaparte, Cat. Met. Ucc. Eur. 1842, 



80. Bonaparte, Rev. Crit. Degland's Orn. Eur. 1850, 202. Thompson, 



Nat. Hist. Ireland, iii. 1851, 392. Bonaparte, Conspectus Avium, ii. 



1856. 207. Des Murs, Traite d'Oologie Ornith. 1860, 551. 

 Stercorarius pomarinus, Vieillot, Nouv. Diet. d'H. N. xxxii. 1819, 158. Vieillot, 



Fauna Franq. 1828, 387. Selys-longchamps, Fauna Belg. 1842, 155. 



Degland, Ornith. Europ. 1849, ii 291. Gray, Genera Birds, 1849, iii. 



652. Lawrence, General Report Birds N. A. 1858, 838. Coues, Proc. 



Acad. Nat. Sc, Philada., 1861, p. 243. 

 Cataractes pomarinus, Stephens, Shaw's Gen. Zool. 1825, xiii. 216, pi. 24. 

 * Macgillivray, Man. Brit. Orn., ii. 1842, 256. 

 Coprotheres pomarinus, Reichenbach, Syst. Av. 1850, 52, pi. 328-9. 

 Catarractes parasita, var. camtschatica, Pallas, Zoograph. Rosso-Asiae, 1811, 



ii. 312. 

 Habitat. Seas and sea coasts of Europe, Asia and North America. Interior 

 of Arctic America. 



I will notice the stages of plumage of this species, from that of the fully 

 adult to that of the young of the year. Having a very extensive series at 

 command, I have endeavored to trace one stage from another, and point out 



1863.] 10 



