50 Birds of Colorado 
more awkward on land, they swim and dive with greater 
facility. The sexes are, as a rule, unlike. 
KEY oF THE GENEBA. 
a. Tail more than half the wing, the feathers stiff and their 
bases hardly hidden by the short coverts. 
Erismatura, p. 64. 
b. Tail normal 
at 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 culmen. Clangula, p. 56. 
b?_ Anterior edge of the nostril behind the middle of the 
culmen. 
at Upper mandible widest behind the nostril, and not 
elevated or swollen at the base. 
a5 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. 
bt 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, rising 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. 
