COLYMBIB^. 191 



Hydromis natator, Milne- Edwards '. 



Hah. Europe (France). 



From tlie Lower Miocene (Upper Oligocene) of Allier. 



Suborder XVII. PYGOPODES. 



Schizognathous birds, with moderately long or short wings, the 

 beak comparatively straight and often much compressed, the tem- 

 poral fossae of the skull separated only by a thin ridge, the angle of the 

 mandible truncated, no ectepicoudylar process to the humerus, aud 

 an upward extension of the cnemial crest of the tibia, which may 

 anchj'lose with the patella. 



The skull has very large supraorbital grooves, which are only 

 separated in the middle line by a narrow ridge. 



The tarso-metatarsus is comparatively short, with a sharp ridge 

 on the outer border of the anterior surface, and the second trochlea 

 relatively shorter and more reflected than in the Tubinares ; the 

 talon may or may not contain a closed tube. 



The tibio-tarsus is readily characterized by the upward extension 

 of the cnemial crest, and the general absence of an ossified bridge 

 over the extensor groove, which is very deep aud wide ; the anterior 

 intercondylar gorge is wide, and the posteiior distal trochlear sur- 

 face short and wide, with prominent lateral ridges. The length of 

 the femur varies considerably iu the two families. 



The coracoid is more or less expanded distally, and always has a 

 large and very prominent hyosternal process placed considerably 

 above the posterior sternal angle ; and the large subclavicular pro- 

 cess is perforated at the base. 



The humerus varies greatly in length ; it always has a long and 

 prominent delto-pectoral crest and a protuberant bicipital surface ; 

 while there is no ectepicoudylar process or subtrochanteric foramen. 



Family COLYMBID^. 



The tarso-metatarsus is much compressed laterally (most so in 

 j Cohjmbus), and has the talon very prominent, with one or more 

 [ closed tubes for the flexor tendons. The tibio-tarsus is at once 



characterized by the anchylosis of its cnemial crest to the patella, 

 \ to form a long spine-like process, and the femur is short, and in the 



type genus much curved. 



' Oiseiiux Fossiles de la France, vol. i. p. .%2 (18(>7-68). 



