488 Remarks on Mr. EytorCs 



racters, to belong to the sub-genus Xema, we must unite the 

 two sub-genera Rissa and Xema, as having no characters to 

 separate them. As to Rissa wanting the hind toe, and the 

 tarsi being moderate, these can never be urged as distinctions, 

 for nothing is mentioned either of toes or tarsi among the 

 characters of Xema, the only given character, " tail forked, " 

 being evidently thought quite sufficient. 



Leaving Xema for an instant, we will examine the author's 

 own sub-genus Chroicocephalus, which, to say the truth of it. 

 is by far the best of the groups, with the exception of Larus, 

 He says, " Under the sub-genus Larus, there has generally 

 been placed two distinct forms, which appear to us to require 

 further subdivision ; we therefore propose the name of Chro- 

 icocephalus, (derived from two Greek words, k%oiko$, coloured, 

 and H£<pahYi, head, signifying that the birds classed under that 

 name have coloured heads), for a new sub -genus under Larus, 

 Linn., for the reception of such gulls as have the tarsi slen- 

 der, thighs considerably denuded, hind toe very small, head 

 only, or head and upper part of the neck, dark coloured in 

 the summer plumage." And again, "The general contour of 

 these birds, (those belonging to the sub-genus Chroicocepha- 

 lus), is much lighter than that of Larus ; they generally feed 

 on the edge of the water, sometimes wading, for which their 

 partially naked thighs peculiarly adapt them." Now here we 

 have a perfect sketch of the habits of the sub-genus Xema, 

 or at least of the type of the sub-genus, the sabine or forked- 

 tail gull, as detailed by Capt. Sabine in the volume of the 

 Linnean Transactions already quoted ; indeed the habits of 

 the one would pass for those of the other without any altera- 

 tion whatever, at least as given by those two gentlemen. You 

 will perceive, from what I have just quoted from Mr. Eyton's 

 work, that his sheet-anchor is the colouring of the head in 

 the summer plumage in Chroicocephalus, and the head being 

 white both in the summer and winter plumage in L.arus : this 

 opinion, if any doubt existed, would be confirmed by his name, 

 which of course explains the most prominent character ; and 

 you will also observe that he thought the form of the tail of 

 so little importance, that it is not mentioned at all until we 

 find it placed among the characters of the sub-genus which 

 I have mentioned above. It is somewhat singular that the 

 original describer of the Larus Sabini, says a it will naturally 

 fall into the division of the gulls with the black heads," and 

 in this I think my readers will entirely agree with him ; for 

 on examination we find that there is absolutely no character, 

 with the exception of the difference in the forms of the tails, 

 to separate them, and this form of the tail T have shewn to 



