76 AVES. 



almost entirely closed by a large naked membrane: wings 

 short, narrow, and acuminated ; first and second quills equal, 

 and longest : tail short, of sixteen feathers. 



105. ALCA Bill a little shorter than the head, rather 



longer than high, much compressed, cultrated ; both man- 

 dibles laterally sulcated ; upper one hooked at the extre- 

 mity ; lower one with the gonys ascending, the mental 

 angle prominent and rounded : nostrils marginal, nearly 

 concealed by the advancing fronfal feathers: wings short, 

 and narrow : tail short, of twelve to sixteen feathers. 



IV. PELECANID^E. Bill strong, sometimes com- 

 pressed; the tomia denticulated : wings long, and 

 powerful: legs very short, in or near the equi- 

 librium : feet with four toes, all united by one 

 continuous membrane. 



106. PHALACROCORAX. Bill a little longer than 

 the head, straight, compressed, culmen rounded ; upper 

 mandible with a longitudinal furrow on each side, the 

 dertrum distinct and strongly hooked ; lower one with the 

 tip truncated : nostrils concealed : face and throat naked : 

 tibia? feathered : middle claw with the inner margin denticu- 

 lated : wings moderate ; first quill shorter than the second, 

 which is longest : tail rounded. 



107. SULA. Bill a little longer than the head, robust, 

 straight, large at the base, compressed and attenuated to- 

 wards the tip ; culmen rounded ; upper mandible laterally 

 sulcated, the tip slightly hooked: gape extending beyond 

 the eyes : face naked : nostrils concealed : tibiae naked at 

 bottom : middle claw with the inner margin denticulated : 

 wings long, and acuminated ; first quill longest, or equal to 

 the second : tail graduated. 



V. LARID^. Bill without denticulations : wings 

 very long : legs in or near the equilibrium : 



