1866.] PROF. W. LILLJEBORG ON THE CLASS OF BIRDS. 9 



it of its most distinguishing character. They seem also to cause 

 confusion if they are arranged within either of the orders Passeres 

 or Zygodactyli ; and we have therefore considered it right to arrange 

 them as a distinct order — Strisores, which name was given to them 

 by Cabanis in 1847. However distinct they seem to be, as well from 

 the Columbine section and the Birds of prey as from the Zygodactyli, 

 it is very difficult to find any character that sharply and distinctly 

 distinguishes them from these three orders ; and we have been com- 

 pelled to use a character in the scheme that does not belong to all, 

 although the majority of them possess it. They appear to be an 

 intermediate group between Accipitres, Zygodactyli, and Passeres. 



The order Longipennes has generally had a very changeable place 

 in the system, sometimes the first among the swimmers, sometimes 

 the last. When the swimmers are, as here, arranged in two groups 

 according to the form of the beak, their place is, as will be seen 

 from the scheme, unquestionable, as we of course must begin with 

 the Pygopodes. The Longipennes approach these very nearly in 

 the genera Pvffinus and Halodroma. Pvffinus has, together with 

 Colymbus and Podiceps, a long pyramidal erect process at the upper 

 end of the tibia, and the tarsi are compressed like theirs. The 

 genera Phalacrocorax and Mergus form an intermediate link between 

 the Steganopodes and the Lamellirostres. 



First Division or Subclass. 

 NATATORES, Illiger ; Sundevall. 



Upper part of the crus (tibia and fibula) not free, but drawn in 

 within the skin that covers the body*. The basis of the hind toe 

 above that of the anterior toes, the hind toe sometimes absent. 

 Legs short ; and the anterior toes, sometimes even the hind toes, 

 united by web. The upper large wing-coverts of the first row on 

 the lower arm (antibrachium) extend in all beyond the middle of 

 the cubital quills. All, with the exception of Podiceps, have, as far 

 as is known, two carotides communes. 



Group 1. SIMPLICIROSTEES. 



The bill without lamina?. Doubly monogamousf. "Altrices ;" 

 that is, carry food to their young. 



Order 1. Pygopodes, Illiger. 



The legs are placed far back ; and the hind toe is, when it is pre- 

 sent, free. The wings short, hardly extending to the base of the tail. 

 The tail short, or none at all. Heavy, clumsy birds, that dive well, 

 but walk badly. 



Note. — This order contains the typical forms of Natatores. 



* Some of the Longipennes are said to form an exception to this, 

 t Both the old ones sit on the eggs, take care of the young, and carry food to 

 tbem. 



