412 NATATORES. 



and yet without ever appearing to pause on their rapid 

 and circular flight. 



Two other species of tern have been observed as occasional 

 stragglers on the coast of Ireland : 



THE NODDY (Sterna stolida), 



Which is blackish brown, with the upper part of the head 

 white, and the tail not forked, and of the same -length as the 

 closed wings. It is naturally a very seaward bird, and often 

 alights upon ships in so exhausted a state as to be easily 

 captured. 



THE ARCTIC TERN (Sterna arcticci), 



Which has the upper part of the body bluish grey ; the 

 forehead, crown, and long feathers on the nape, black ; the 

 neck, the belly, and the under tail-coverts pure white, and 

 the feet and bill (which is very slender) red. The tail is 

 very much forked, and the entire length about thirteen 

 inches. This species, as the name implies, inhabits the 

 Northern Polar Seas, and it is found in every longitude 

 where those seas are accessible. 



PETRELS. 



There are three modern genera of birds, which may be 

 included under the common English name of Petrels, pro- 

 cellaria, puffimts, and tJialassidroma. They are all birds of 

 the high seas, ranging far both in latitude and in longitude ; 

 and the numbers of some of the species, particularly in the 

 southern hemisphere, are beyond all counting. They are 

 also birds of powerful flight, and have the feet equally well 

 adapted for swimming or for bearing them up on the surface 

 of the water. The toes are very long and the webs extended, 

 so that the birds move along the surface as if they were 



