8/2 The American Naturalist. [October, 
AA. Toes two in front (heterodactylous). 
Toes free ; hallux well developed ; basiptery golds 
present ; Trogonoidei. 
III. Maxillopalatines not united on median line ; vomer sin- 
gle, truncate, and excavated in front. {ALgithognathcB^ 
A. Toes three in front (anisodactylous). 
Toes free ; hallux well developed ; tarsometa- 
tarsus with five tendinous canals ; basiptery- 
goids wanting or rudimental ; sternum with 
two notches ; no caeca coli ; one carotid artery ; Passeres. 
AA. Four toes directed forwards (pamprodactylous). 
Toes free ; no basipterygoids ; sternum entire 
posteriorly ; tensor patigii brevis muscle at- 
tached to a tendon which extends to the 
man us ; no cceca ; Micropodioidei. 
IV. Maxillopalatines separate ; vomer dou- 
ble, represented by two lamince. (SaurognathcB) 
A. Two toes directed forwards. 
Feet zygodactylous ; no ccEca coli ; no inter- 
clavicle ; one carotid artery ; Picoidei. 
The arrangement of the above orders is not expressive of their 
true affinities in all cases. Thus the Cohoidei, Cocygomorphae, 
Micropodioidei, Trogonoidei, and Picoidei, are more or less re- 
lated, and sometimes brought together into a single heterogeneous 
order called the Picariae. 
The families of the Euornithes are as follows : 
Stegatiopodes ; Phaetonidae, Fregatidae, Pelecanidae, Sulidae, Pha- 
lacrocoracidae, Plotidae. 
ChenomorphcE ; Palamedeidae, Anatidae, Phoenicopteridae. 
Hcrodii ; Ibididae, Ciconiidae, Balaenicipitidai, Ardeidae. 
Accipitrcs ; Cathartidae, Falconidae, Pandionidai, Strigidai. 
Psittaci; Psittacidai. 
CecomorphcE ; Colymbidae, Heliornithidas, Alcidae, Laridae, Pro- 
cellariidae. 
GrallcB ; Chionidae, Thinocoridae, Glareolidae, Dromadidae, 
Charadriidae, Otidid^E, Eurypygiidae, Rhinochetidae, Caria- 
midae, Psophiidae, Gruidae, Rallidae. 
