432 NATATORES. ALCA. 



white, mixed more or less with black. In other respects 

 there is little or no difference. 



GENUS ALCA, LINN. AUK. 



GENERIC CHARACTERS. 



BILL shorter than the head, nearly as deep as long, much 

 compressed, cultrated; with both mandibles laterally sul- 

 cated; tip of the mandible strongly arched, and hooked; 

 that of the under one obliquely truncated ; angle deep, and 

 ascending. Nostrils near the lower edge, and immediately 

 behind the horny part of the bill ; nearly hidden by the fea- 

 thers of the antia, or projecting side-angles of the forehead. 

 Head narrow, and attenuated in front ; with the antiae reach- 

 ing as far as the nostrils. 



Wings short and narrow ; and in one species unequal to 

 the purpose of flight. Tail short ; of twelve or sixteen fea- 

 thers. 



Legs short, situated at the posterior part of the body, and 

 having the tibiae hidden within the integuments of the abdo- 

 men. Feet with three toes, all directed forwards, and web- 

 bed ; outer toe longer than the inner, and nearly equal to the 

 middle one. Claws hooked, and sharp ; the middle one the 

 largest and longest. Front of the tarsus and the toes scutel- 

 lated. 



In this genus the bill becomes strongly compressed and 

 hooked, losing that character of breadth at the base pos- 

 sessed by Mergulus, and by TEMM INCH'S genus Phaleris. 

 The lateral furrows of the bill are also more distinct, in 

 which respect these birds approach to the succeeding genus 

 Prater cula (Puffin). Their wings are very short and nar- 

 row ; in one species, indeed, the Great Auk (Alca impennis)^ 

 they are so imperfectly developed as to be totally unfit for 



