LARID.E — THE GULLS AND TEllNS — IIYDUUCHELIDON. 317 



hh'd" par excellence, and is more or less confounded with the S. fallfjinosa. Mr. Law- 

 rence, in his paper on the Birds of Sombrero — a rocky iskit near St. Martin's — 

 quotes Mr. Julien as believing that the number of individuals of this species which 

 visited that place was at one time equalled only by those oi S. maxima and Anous 

 stolldus. It is said to be remarkable for its social peculiarities — almost always asso- 

 ciating with the Noddies ; and in however great numbers it may be present on any 

 Key, it is found to be almost always more or less mixed with flocks of that Tern. 

 It arrives at Sombrero in March, and departs in August. Its nest is said to be similar 

 to that of the Noddy, and it lays but one egg. It often flies high, and with a pecu- 

 liarly quick darting motion, keeping up a noisy chattering very different from the 

 discordant " caw-caw " of Anous stolldus. Mr. Julien never observed the two species 

 to quarrel with each other, although individuals of the same species often engaged in 

 long and obstinate combats. 



The eggs of this bird found at Sombrero are described by Mr. Lawrence as meas- 

 uring 1.88 inches in length by 1.25 in breadth, as having a ground-color of a creamy 

 white, and as being marked with blotches of deep rusty brown, most abundant on the 

 larger end. Eggs collected in British Honduras by Mr. Osbert Salvin vary in length 

 from 1.90 inches to 1.85, and in breadth from 1.35 to 1.30. Their ground-color is pale 

 brownish cream, and the markings are small spots of burnt-sienna and lavender-gray. 



Mr. Cory found birds of this species breeding in large numbers at Clarence Harbor. 

 They were in company with the Sooty and the Roseate Tern ; and eggs procured as 

 late as June 8 were quite fresh. In their breeding habits jNIr. Cory found them very 

 similar to the fidif/hiosa. Their eggs were found deposited in slieltered clefts in ledges 

 of rocks, or in cavities among the loose bowlders which lined the sea-shore. The egg 

 in all instances was single, and resembled that of the fuliginosa, but was more 

 spotted about the larger end, while the reddish tinge of the ground-color was much 

 fainter. The egg taken by Mr. Cory measures 2.00 inches in length by 1.42 in 

 breadth ; the ground-color is a rich cream, strongly washed with a rufous tint ; 

 around the larger end is a ring of large and confluent blotches of reddish brown ; 

 smaller spots of the same are diffused in a scattered manner over the whole egg, with 

 obscure shell-markings of lilac and slate. 



An egQ in my collection, taken by Mr. Godeffroy on the coast of New Guinea, 

 measures 2.05 inches by 1.45. The ground-color is pure cream, without a tinge of any 

 other shade. Grouped around the larger end, covering nearly the entire portion, are 

 numerous spots of light brown, and others of much deeper shade, interspersed, and 

 occasionally confluent. Smaller ones are sparingly scattered over the entire surface, 

 and there are also a few shell-markings of a faint purple. 



Gexus HYDROCHELIDON, Boie. 



Hydrochdidon, Boie, Isis, 1822, 563 (type, Sterna nigra, Linn.). 



Char. Similar to the smaller species of Sterna, hut tail only very slightly forked or emargi- 

 Tiate, the rectrices not attenuated at ends, and the webs of the toes filling less than half the inter- 

 digital spaces. Adults gray or blackish Ijeneath, as dark as, or darker than, the color of the upper 

 surface. 



The three known species of this genus may be defined as follows — ?I. Irucoparin being included, 

 partly for comparison, but more especially on account of having been obtained in the West Indies, 

 and therefore entitled to a place iu the American iauna : — 



