COLYMBI 391 



large number of complete ribs as more archaic characters 

 than the reverse ; the other features as evidence of degenera- 

 tion require no comment. 



In considering, then, the affinities of the Colymbi the 

 Colymbida? are to be chiefly taken into account. But any 

 comparisons bristle with difficulties. The late Mr. FORBES 

 in his final scheme of classification definitely associated the 

 Colymbi with the Heliornithidae ; in this course I supported 

 him by reason of certain muscular characters of both groups 

 of birds. The outward appearance, too, of both birds is not 

 at variance with such an affinity. The muscular formula of 

 the leg is the very unusual one of ABX + . This reduced 

 formula is found in Podoa and in the Sphenisci, Anatida?, 

 Tubinares, Plialacrocorax, and certain Alcidae. It is to be noted 

 that all of these are at least largely aquatic in their habits, a 

 fact which must, of course, discount the value of the character ; 

 but still ABX is an unusual formula, and there are other 

 grounds for regarding the birds mentioned (with the excep- 

 tion, perhaps, of the Alcida?) as having some relation to each 

 other. The insertion of the biceps slip on to the patagium 

 allies Colymbus and Podoa ; though this also occurs in other 

 birds, it is, again, in some that are presumably not far from 

 the Colymbi : for example, of the forty characters selected 

 by GADOW for the comparison of the various groups of birds 

 the Colymbidae agree with the Sphenisci in twenty-eight ; 

 with the Tubinares in twenty-seven ; with the Steganopodes in 

 twenty-six ; with the Anatidae in twenty-three ; with the 

 Heliornithidaj in twenty-three. 



On the other hand there are twenty-five points of likeness 

 to the Laridse, as deduced from the same tables, and no less 

 than twenty-nine to the Alcse. As might indeed be imagined, 

 it would be rash to lay much stress upon the proportions of 

 these numbers. It is not to my mind clear with which of 

 the groups mentioned the Colymbi are most nearly allied. 

 Their undoubted relationship to the Hesper or niches is treated 

 of on another page (p. 395) ; and it is perhaps this very fact 

 which prevents us from detecting likenesses to more modern 

 (?) groups. 



