50 Birds of Colorado 



more awkward on land, they swim and dive with greater 

 facility. The sexes are, as a rule, unlike. 



Key of thk Genera. 



a. Tail more than half the wing, the feathers stiS and their 



bases hardly hidden by the short coverts. 



Erismatura, p. 64. 



b. Tail normaL 



a^ Feathering on the lores or forehead not reaching beyond 

 the posterior border of the nostrils. 

 a* Graduation of the tail less than the length of the bill 

 from the nostril. Marilla, p. 50. 



b* Graduation of the tail more than the length of the bill 

 from the nostril. 

 a' Anterior edge of the nostril in front of the middle of 

 the culmea. Clangula, p. 56. 



b* Anterior edge of the nostril behind the middle of the 

 culmen. 

 a* Upper mandible widest behind the nostril, and not 

 elevated or swollen at the base, 

 a* Feathers ending in a straight line across the 

 forehead. Harelda, p. 59. 



b^ Feathers ending in an acute-pointed triangle 

 on the forehead, 

 a^ Upper mandible constricted to a small nail-like 

 tip. Charitonetta, p. 58. 



b' Upper mandible rounded at the tip. 



Histrionicus, p. 60. 

 b* Upper mandible widest at anterior edge of nostril, 

 and elevated or swollen at the base. 



Oidemia, p. 62. 

 b^ Feathering on the lores or forehead extending forward 

 >> well beyond the posterior border of the nostril. 



Somateria, p. 61. 



Genus Marila 



Bill of ordinary shape without any special swellings or gibbosities, 

 about as long as the head, rLsing high at the forehead ; nail distinct, 

 about one-third the width of the end of the bill and decurved ; tail 

 short and rounded, graduated less than the length of the bill from 

 the nostrils, of 14 to 16 feathers ; tarsus less than two-fifths length of 

 the middle toe and claw ; head not crested ; speculum white or grey. 



A large cosmopolitan genus with five North American species. 



