1890.] 



ANATOMY OF PODICA SENEGALENSIS. 



433 



He does not, however, direct attention in the skull to all the 

 points which I refer to in the following brief enumeration of the 

 characters which distinguish the Grebe from the Rails. 



In the Rails the maxillo-palatines are large, and are not concealed 

 by the underlying palatines when the skull is viewed from below \ 



In the Grebe, the maxillo-palatines are very slight curved plates 

 of bone, which are almost entirely concealed by the underlying 

 palatines, only projecting very slightly on the inner side of these 

 bones. 



In the Rails the cranial axis extends as far forward as (at least) 

 the middle of the maxillo-palatines. In the Grebes it does not 

 reach the posterior margin of these bones. 



Skull of Podica senegalensis, lateral view ; nat. size. 



In the Rails the temporal fossa is not bounded by very sharply 

 marked ridges ^ ; in the Grebes it is so marked, particularly in 

 Podiceps cornutus and P. cristatus ; in P. minor this character is less 

 obvious. 



The temporal fossce themselves are much more extensive in the 

 Grebes than in the Rails. 



The occipital condyle in the Rails is round ; in the Grebes it is 

 decidedly kidney-shaped with the " hilum " above. 



The forward process of the quadrate'' is more slender in the 

 Grebes than in the Rails. 



The general outline of the skull from above appears also to be 

 very characteristic in these two groups. The hinder part of the 

 skull is rhomboidal in the Grebes, and squarish in the Rails ; this is 

 due to the peculiar development of the temporal fossae, which are 

 quite visible from above, while the jutting-out region of the skull 



^ In the shape of its maxiUo-palatines, Fidica comes nearer to Podiceps than 

 do either Oci/dromvs or Crex ; they are curved and comparatively tliin in 

 Fidica, instead of being inflated bulla as in the two latter genera. 



- In Ocijdromus ausfralis this ridge is rather more marked than in Fidica, 

 Crcx, and Aramides ; it is curious to note there is not any approximation here 

 to the Grebes through P. minor. In the Eail it is the commencement of the 

 ridge which is best marked, in the Grebe the middle portion. Giebel has re- 

 marked that Podiceps minor is less of a typical Grebe than is, for example, 

 Podiceps cristafus ; but he does not refer to this particular point. 



^ Special attention has been lately directed to the quadrate as furnishing 

 evidence of particular affinities in an interesting paper by Miss Walker (Studies 

 from the Mus. of Zool. Univ. Coll. Dundee, vol. i. no. 1). 



