ORDERIV. 
RASORES. 
Cr.—Bill not longer than the head ; the terminal portion more or less vaulted, hard, with or without a soft skin intervening 
between it and the head. Nostril with an overlapping fleshy or leathery scale or valve extending over its upper edge, 
In the table on page 2 of the present report I have given a synoptical view of such orders 
as belong to the United States, borrowed chiefly from Keyserling and Blasius. This, however, 
will be found to contain several important errors, especially in reference to the position of the 
hind toe. This is stated to be raised above the level of the rest in Rasores, Grallatores, and 
Natatores, and such is generally the case; but in the Columbae and Penelopidae, of the first 
order, and the Ardeadae, of the second, it is inserted either nearly or quite opposite the others, 
This is only one of the many illustrations of the difficulty of expressing the characters of the 
primary groups in ornithology by a single concise phrase, the transition from one to the other 
being so gradual as to render it almost impossible to say where one ends and another begins. 
In the table just referred to, and in the arrangement and succession of the higher divisions 
of the volume, I have not pretended to follow the more recent ideas of Bonaparte and others. 
My object was merely to indicate the North American species of birds, especially those collected 
by the government expeditions, with their range and distribution, and not to attempt any of the 
higher generalizations. For this reason I have followed the older division into orders, although 
that of Bonaparte in many respects is more philosophical. This author arranges birds into two 
sub-classes, called Altrices and Praecoces, accordingly as their young require to be brought up in 
the nest, or are able to run about immediately after birth and gather food for themselves. 
Each of these sub-classes is divided into orders, which range in parallel series, as shown in 
the accompanying table, taken from volume XX XVII of Comptes Rendus, for October 31, 1853. 
It will be seen from the table that the Inepti (dodo, &c.,) of the Altrices represent the Séru- 
thiones (ostriches) of the Praecoces; the Gyrantes, or true doves, the gallinaceous birds; the 
Herodiones, or herons, &c., the Grallae (sandpipers, snipes, &c.); the Gaviae, or gulls, pelicans, 
&c., the Anseres, (ducks, grebes, penguins, &c.) The parallelism in this case corresponds, to a 
certain degree, with that which prevails in the mammals between the MMarsupiata and the 
Placentalia, and the time will probably come when naturalists will as little think of mixing up 
the Altrices and Praecoces in the same order, as they now do a similar combination of the 
marsupial and non-marsupial mammals. 
The position of the hind toe seems to have a direct relationship to the mode of life of the 
bird. Those species which live on or among trees, and especially which nest and bring up their 
young there, have the hind toe elongated, and placed low down more or less on a level with the 
anterior ones, apparently to facilitate prehension. Such we see to be the case in the herons, and 
a few other arboricole waders, and in the Penelopidae and Jlegapodidae of the gallinaceous 
birds. Some of the doves exhibit a tendency to an elevation of the hind toe; this, at any rate, 
appears to be the case in Starnoenas. 
July 1, 1858. 
75D 
