ALC/E 



365 



table it seems possible to divide the group into two families, 

 Uriidae and Fraterculida 3 , which maybe thus defined :- 



Uriidae. 



Rectrices, twelve or fourteen. Lobes of liver equal, 

 or left larger than right. Muscle formula, 

 ABX- (or AX-). 



Fraterculidae. 



Hcctrices, sixteen. Lobes of liver equal, or right 

 larger than left. Muscle formula, AX+. 

 Syrinx peculiar. 



Syrinx 



With U-shaped first 

 broiichial semi-ring 

 With U-shaped first 

 bronchial semi-ring 



With U-shaped first 

 bronchial semi-ring 



There appears to me to be no doubt that the Alcae are 

 best placed in the neighbourhood of the Limicolae, though, 

 as FUEBEINGEE justly states, ' at first sight the relations 

 between the two groups do not appear to be intimate.' 

 These differences, however, merely concern outward form, in 

 which it is perhaps reasonable to compare the auks with 

 the grebes. But an anatomical study shows plainly that 

 the grebes are much further away from the auks than are 

 the Limicolae. Such points of likeness as there are with the 

 Colymbi are largely, if not entirely, due to the similar life ; 

 thus the elongated sternum, which is also shared by the 

 aquatic ducks, and possibly the muscle formula ABX + . 

 With the Limicolae are many positive points of likeness, to 

 which no such explanation seems to be applicable. In the 

 skull it is hard to find points of difference ; but the most 

 remarkable point of similarity is the presence in both groups 

 of those additional tendinous slips upon the patagium on the 



