36 Field Museum of Natural History — Zoology, Vol. IX. 



♦GROUP 1. Wing, Jess than 6.50 inches long. 



Depth of bill at base of culmen, over .40. Upper parts, glossy 

 brownish black; sides of body and neck, tinged with brown, belly 

 white. 



In summer: Bill, with black band; throat, black. In winter: 

 Bill, without black band; throat, white. Podilymbus podiceps. 



Pied-billed Grebe. Hell Diver. 

 See No. 5. 



Depth of bill at base of culmen, less than .40 ; upper mandible, 

 nearly straight and decidedly flattened at nostril; under mandible, 

 straight for about three-fourths of its length and then sharply 

 ascending. Colymbus nigricoUis calif amicus . 



American Eared Grebe. 

 See No. 4. 



Depth of bill at base of culmen, less than .40; top of upper 

 mandible (culmen), curved and not flattened at nostrils; under 



mandible, not as sharply ascending near 

 the tip. While the summer plumages of 

 californicus and auritus are very different, 

 the winter plumages are similar. 



In summer: Two small tufts of grayish- 

 brown or buff-colored feathers, behind the 

 eye; crown, nape, and throat, black. 



In winter: Plain colored, without black or 

 buff on head; upper plumage, grayish 

 black; under parts, silvery white, often tinged with ash gray on 

 throat and sides ; no developed plumes behind the eye. 



Colymbus auritus. 

 Horned Grebe. 

 See No. 3. 



* GROUP 2. Wing, over 6.50 inches long. 



Nostril to tip of bill, less than 2 inches ; tarsus with middle toe and 

 claw together, less than 5.50. 



In summer: Crown, black; upper throat, gray; lower throat and 

 breast, chestnut rufous; rest of underparts, silvery grayish white. 



♦For directions for measurement, see page 21. 



