NATATORES. STERNA. 461 



age, they float with much buoyancy ; but they make little 

 use of their power of swimming, and are altogether incapa- 

 ble of diving. Others, as the Petrels, never actually alight 

 on the water, but use their webbed feet to run, as it were, 

 upon the surface of the waves ; and in this action they are 

 assisted by their wings, which are kept partly open. The 

 passage from the Pelecanidce to these birds is effected by the 

 near affinity existing between the genus Phaeton of that di- 

 vision and the larger Terns which commence the present 

 one. In this family also, according to the arrangement of 

 Mr VIGORS, a form is found connecting it with the Anatidoe, 

 thus completing the circular succession of the Order ; and 

 this he thinks is performed by Pachyptila, a genus nearly 

 allied to the Petrels. The affinity thus endeavoured to be 

 established, seems, I must confess, distant, and stands in 

 need of the interposition of other forms to render it satisfac- 

 tory and complete. 



GENUS STERNA, LINN. TERN. 



GENERIC CHARACTERS. 



BILL as long as, or longer than, the head, almost strait, 

 compressed, drawn to a fine point, with both mandibles of 

 equal length, and the upper slightly convex. Tomia rather 

 intracted and sharp-edged. Lower mandible having a pro- 

 minent angle near its middle part. Nostrils basal, lateral, 

 linear oblong, pervious. 



Wings very long, acuminate, with the first quill-feather 

 the longest. Tail more or less forked. Legs having the 

 tibiae naked for a short space above the tarsal joint. Tarsi 

 short. Feet of four toes, three before and one behind ; the 

 three front toes united by a membrane more or less scalloped, 

 the hind toe small and free. Claws arched and sharp. 



The Terns, which, in the present family, appear to repre- 



