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Show (j,'38 MR. H. SAUNDERS ON THE STERNINA. [Jlllie 20, 6. On the Sternina, or Terns, with Descriptions of three Species. By H O W A R D SAUNDERS, F.L.S., F.Z.S. [Received June 6, 1876.] (Plate LXI.) Having recently had opportunities of examining some interesting types of various real and supposed species of the subfamily Sternina, I propose to anticipate to a certain extent the monograph of the Larida upon which I have been for some time engaged, and to give the result of m y observations in the following review of the species at present known to me, with general remarks upon their geographical distribution. The principal writers who have hitherto treated of the Sternina are:-Prof. Schlegel, in the Mus. d'Hist. Nat. Pays-Bas, Sterna, 1863 ; Prof. Blasius, in Journ. fiir Orn. 1866, p. 73 ; Dr. Elliott Coues, in Proc. Phil. Acad. 1862, and monographically, as regards the North-American species, in his ' Birds of the North West' 1874 ; and Messrs. Sclater and Salvin (Neotropical Laridse, P. Z. S. 1871). And from the works of these able authors I have derived much assistance, especially from the last, owing to the care with which the synonymy and the geographical distribution have been worked out. Indeed as regards America I might well have been content to wait until the completion of m y monograph; but as there are a good many species in other parts of the globe which have not been so recently noticed, there may be room for a few remarks. It is almost needless to say that, owing to the general similarity in colour, the Sternina are a. troublesome subfamily to handle, the question of what constitutes specific distinctness being here more than usually perplexing. The individual differences in size of bill, length of wing, &c. are often considerable ; added to which there are subtile gradations in the various shades of plumage, which render it impossible to accord specific rank to forms which, when judged by their extremes alone, seem totally distinct. Under these circumstances it is not surprising that a species should sometimes be based upon what may appear at the first glance to be a very slight distinction ; for the alternative is to unite under one head some forms which are clearly different; and considering the general tendency that there is towards blending, the systematist must be glad to avail himself of the smallest permanent characteristic. The young are often very much alike ; and indeed in several cases they are as yet undistinguishahle with the limited material at present available; but larger series of authentic specimens will doubtless clear up several points. The coloration of the soft parts presents considerable difficulties, owing to the changes which take place at different ages and seasons, it frequently happening that the bill and legs in quite young birds increase in intensity of colour up to a certain time in autumn, and then become dark, the brighter colour not being resumed until the following spring : this is notably the case with the Common and the Arctic Terns, in which the bills become dark very suddenly between the |