THE TUBINARES. 143 



3. Larus. The smaller species of this genus, such as L, minutus, ridibundus, and canus, 

 have precisely the pterylosis of Sterna; but in the larger species, such as L. argentatus, 

 tridactylus, eburneus, and marinus, the tract-bands appear perceptibly broader, although exactly 

 similar in pattern, from which it follows, as a matter of course, that the spaces must be of less 

 extent. Nevertheless, the outer branch and main stem of the inferior tract are not partially 

 coalescent, but, on the contrary, the space separating them is broader in proportion than in 

 Sterna. I found down-feathers all over the body, even decidedly between the contour-feathers. 

 Even upon the body of the oil-gland, which is not very large, there are several rows of semi- 

 plumes. The mamilla of this gland is somewhat longer than in Sterna, and has three orifices in 

 each half; these open close together in a bowl-shaped depression. I found this structure 

 in L. marinus and tridactylus, and believe we may assume that the same occurs in all other 

 species of Larus. Of the species examined L. minutus had twenty-eight remiges, L. ridibundus 

 thirty, L. canus and tridactylus thirty-one, L. argentatus and marinus thirty-four. In all there are 

 ten on the pinion, and the first is the longest throughout. The number of rectrices is twelve. 



4. Lestris. This genus differs from the other Longipennes especially in having the outer 

 branch of the inferior tract united with the main stem in the first part of its course (PI. IX, 

 fig. 13), and all the tracts still broader and stronger than in Larus. In L. catarrhactes and 

 pomarinus the dorsal tract agrees with the type of the Longipennes, although its longitudinal space 

 is proportionally broader, on account of the stouter formation of the thorax in the Skuas. Hence 

 also, probably, it happens that the lumbar tracts are placed more obliquely than in the Gulls, and 

 coalesce posteriorly with the uropygial band of the dorsal tract (PL IX, fig. 14). I have already 

 mentioned with regard to L. parasiticus that the anterior part of the dorsal tract is not dis- 

 tinctly separated from the posterior. I may add that the arms of the former pass directly 

 into the two branches of the latter, thus producing a form which appears to be very similar to 

 the type of the Hallince (see p. 125). Combined with this is an increased separation of the outer 

 branch from the main stem of the inferior tract. All three species have twelve tail-feathers, and 

 from twenty-six to twenty-eight remiges, of which ten are situated on the pinion, and the first is 

 the longest. In Lestris catarrhactes the large oil-gland agrees perfectly in structure with that of 

 Larus marinus : it has semiplumes on its surface, but only at the base ; a very broad, short 

 mamilla, and three orifices in each half. 



2. NASUT^E seu TUBINARES. 



In this family the tract-formation of Lestris is elevated into the type of a group, undergoing 

 scarcely any change in the form of the inferior tract, but showing some little modification in the 

 dorsal tract. We find, therefore, on the head, a uniformly dense plumage, from which the two 

 principal tracts issue. The latter are separated from each other by the lateral neck-spaces, which 

 extend high up, nearly to the head. The inferior tract is divided near the head, becomes of con- 

 siderable breadth whilst still on the neck, and passes in this condition on to the breast, the 

 surface of which is covered by each band in a rather broad, parallel-sided form, emitting no 

 branch as far as the margin of the musculus pecloralis major. Here it is divided by a space 



