590 LARID^ GULLS, ETC. 



the Audvibonian period, as far as the North American species are concerned. Dr. Bla- 

 sius's review of the family (J. f. O. 186r)-'66) is a very important coutributiou, as is 

 also Messrs. Sclater and Salviu's paper, in the Proceedings of the Zoological Society 

 of 1871, on the Neotropical forms. 



Determination of species in this family is difficult. Without reference to the abstract 

 questions involved of the nature of species, it is practically impo^ssible to re<-oguize or 

 define a considerable number of species which authors holding such views as Bruch and 

 Bonaparte do, have sought to maintain. The same laws of variation under latitude, cli- 

 mate, and other physical influences which hive been proven elsewhere, hold here, re- 

 quiring recognition of various geographical races, rather than species, many forms 

 being found to grade into each other. Further difficulty arises in the circumstance 

 that while the sexes, as a rule if not without exception, of Laridw are alike, the indi- 

 vidual differences in size and ])lumage, according to age and season, are at a high rate, 

 requiring large allowances. Characters must be decided to furnish grounds for species 

 in this £<roup ; and, although very nice distinctions frequently subsist (among Ster- 

 tihice particularly), it must be confessed that every large collection contains doubtful 

 specimens. The shade of the "gull-blue" of the mantle of most species of this fiimily 

 varies within wide limits, according to age and wear of the feathers, season, locality, 

 and even as a j)urely fortuitous circumstance. The pattern of the primaries when 

 marked, as is usual, with black and white in certain areas, is only approximately con- 

 stant for the same age of individual feathers ; for the rest, it is subject to nearly contin- 

 uous progressive changes with age and " wear" of the quills. In their progress toward 

 maturity, young Laridoi are usually subject to a series of changes affecting the color 

 of the plumage and of the bill and feet very materially, as well as the stature. There 

 are also, among the Jaegers, special states of plumage. The moult appears to be always 

 double, vernal and autumnal ; from this result the seasonal changes which are over 

 and above the others referred to ; these are almost always strongly pronounced. The 

 moulting of the wing-quills is always gradually successive, almost feather by feather, 

 so that the birds are at no time deprived of flight. The change may be advantage- 

 ously studied in the Terns, from the heavily-silvered fresh quill to the worn dusky- 

 brown one. The ichite areas on the quills of Gulls and Terns appear to have less vital- 

 ity than those parts which are loaded with pigment, for we frequently find the quills 

 ■worn away according to the pattern of their markings. Some rules of change in 

 plumage are these : Young birds have their own livery ; at first darker than that of 

 the adults, or at least mottled with dark colors ; there may be several different stages. 

 Sexes are alike. Winter and summer vestures are different ; black on the head, and 

 rosy on the under parts, are greatly restricted or wanting in winter; even a black body 

 may be changed to light. In white-headed species, dusky variegation of the head and 

 neck occurs. Ordinarily more than a year is consumed in the progress to maturity ; 

 such is particularly the case with the larger Gulls and Jaegers. 



Anatomical characters are very constant throughout the family. The osteology is 

 almost the same throughout, excejiting the skull of liliynchops ; minor skeletal features 

 are given under several heads beyond. Other peculiarities are nearly confined to de- 

 tails of the digestive system. Of the pterylosis it may be observed, after Nitzsch, that 

 the general character is perfectly scolopacine ; that the tracts and spaces are narrowed 

 in Stermnff, and somewhat peculiar in Lestridinw, there approaching the ProceUariid(e. 

 It is a curious rule (subject, however, to exceptions) that three of the four subfamilies 

 are distinguished by shape of tail — cuneate in Lestridiva, square in Larince, forked in 

 Sternhuv and Ilhyncliop'ma',. 



The bibliography of the family is extensive and involved, though perhaps not un- 

 usually so, and certainly not more so than would be expected in a group where it is 

 difficult to discriminate the species even upon examination of specimens, let alone 

 descriptions. I have done my best in this matter, following the law of priority in the 

 selection of names, excepting only when earlier ones woujd, if used, supersede those 

 Linna'us, and taking this author at 1758. 



More or fewer (in some cases scores) of specimens of all the North American Laridw 

 have been personally examined, excepting these : Ehodostetliia rosea and Xema fiirvatnm. 

 The available material includes a large proportion of types, among them those of Audu- 

 bon, Eichardson, Peale, Gambel, Cassiu, Lawrence, Baird. 



Family LAEID^. 



Cn. Natatores longipennes, naribus perviis, latcralihus, halluce lihro. 



The preceding brief diagnosis distinguishes the Laridw from other families of the 

 yatatores. Anseres and Pygopodes differ in their short wings, &c. ; the Sfeganopodig, 

 which are longipennine, are separated by their totipalmated feet ; while the Frocella- 

 riifla; the associates of Laridw under Lonijipennes, are recognized by the jieculiarities 



