CHAPTER XIII. 



GULLS AND THEIR ALLIES. 



(Longipennes.) 



HE transition from the Auk group to the GnH-grwip is 

 easy and not far to seek. If one will take the skeleton 

 of any one of the typical Murres (Uria) and critically 

 compare it with the skeleton of a typical Gull (Larus), 

 it at once becomes evident that the two genera, although belong- 

 ing to different suborders, are not by any means so far separated 

 but what the relationship is easily recognized. Other structures 

 than the skeleton give support to the facts derived from a com- 

 parison of this kind. Now the Gull group constitutes the sub- 

 order LOXGIPENNES, and so far as our American avifauna is con- 

 cerned, it includes representatives of the skuas, the jaegers, the 

 gulls, the terns, and the skimmers. But one skua is known to 

 occur upon our coast the common one (Megalestris skua), and 

 but three jaegers, all of the genus Stercorariits. The gulls are 

 far more numerous, and are represented by a number of genera, 

 as Gavia, Larus, Rissa, RJiodostethia, and Xema; including in all 

 nearly thirty species, the vast majority of which belong to the 

 genus Larus, which is the typical one. Terns are not quite as nu- 

 merous as the gulls, but there are still nearly twenty species of 

 them belonging to our fauna. They are distributed through the 

 four genera Gcloclidulon, tfterna, TTi/drochelidon, and A nows, most 

 of them belonging to the more typical genus Sterna. Finally, in 

 an entirely distinct family, we have the Black skimmer (Ryn- 

 clwps). 



At different times during the past few years the present writer 

 has made extensive comparative studies of the morphology of 

 this group of birds, and especially of their osteology, and from 

 these investigations has been led to the opinion that the follow- 

 ing scheme of classification expresses the relations of these birds 

 to each other within the suborder. 



) Sternitii 



>M. 



{ RYNCHOPIDJE. 



So far as anatomy goes, and to some extent habit and appear- 

 ance, the gulls merge almost insensibly into the terns, as, for 

 example, the gnll known as Sabine's gull (Xema sabinii) is quite 



