386 STEUCTUEE AND CLASSIFICATION OF BIEDS 



likely that the wings of this bird were more efficieDt than 

 those of the ratites on account of the apparently well- 

 developed remiges. 



COLYMBI 



Definition. — Oil gland tufted. Aftershaft pressnt. Aquinoubital. 

 Accessory semitendinosus abssnt Biceps slip present. Glutseus 

 maximus large, extending beMnd acetabulum. Ceeca long. 

 Skull holorMnal, -without basipterygoid processes, scUzogna- 

 thous. Tibial crest strongly developed. 



This group of birds contains two very well-marked families, 

 the divers (Colymbidse) andthe grebes (Podicipedidae). In view 

 of their numerous and important points of similarity I have 

 not thought it desirable to separate these two families quite 

 so widely as has Gadow. The Colymbidse contain but one 

 genus, Colymhus, with four species. Of the grebes there is 

 perhaps also only one well-marked genus, Podicipes. But 

 the Central American Gentropelma (of Sclater and Salvin.) 

 has some claims, on account of the complete loss of flight, to 

 generic distinction, while in the course of the following pages 

 it will be seen that there are certain, if small, reasons for 

 distinguishing Mchmophorus and Tachybaptes. Podilymbus, 

 another alleged genus, has not been dissected. 



Our knowledge of the anatomy of this group of birds is 

 chiefly due to Nitzsch,' Brandt,^ Coubs,' Shufeldt,'' and 

 myself.^ 



As to external characters, thexe is a close agreement 

 among the Colymbi. The number of rectrices in Colymbus 

 glacialis I find to be twenty. Nitzsch gives eighteen to 

 twenty for the genus. Specialised rectrices are not recognis- 

 able among the grebes. The inferior tract of feathers is 



' hoc. cit. 



2 ' Beitrage z. Kenntniss d. Naturg. d. Vogel,' Mem. Ac. St. Petersb. 1840, 

 p. 197. 



' ' On the Osteology of Colymbus,'' &q,., Mem. Bost. Soc. Nat. Hist. i. 1866, 

 p. 131. 



•• ' Concerning the Taxonomy of the N. Ainerioan Pygopodes,' &c., J. Anati 

 Phys. 1892, p. 198. 



» ' Notes upon the Anatomy of a Grebe {JEchmophorusmajoi-),' &c., P. Z. S. 

 1896, p. 538. 



