1890.] 



ANATOMY OF PODICA SENEGALENSIS. 



439 



project freely as a vertical plate of bone between the two ilia. Giebel 

 states that there is a ridge running as far as the end of the pelvis 

 which marks the boundary between the postacetabular portion of 

 the ilium from the ischium on each side ; I have already contrasted 

 the pelvis oi Podica with that of the Rails by the absence in the former 

 of such a well-marked ridge. In this particular therefore it appears 

 that the Neotropical Heliornis has diverged less from the Rail-pattern 

 than Podica has. 



It is evident, however, from Giebel's description that Podoa offers 

 no veiy great differences from Podica, and that both these birds 

 present a very much closer resemblance in the characters of the 

 pelvis to the Rails than they do to the Grebes or Divers. 



Giebel thus describes the ribs in Heliornis : — 



" Podoa possesses eight pairs of ribs, and of these the first and 

 second are false ribs, without uncinate processes, the following broad 

 and flat, all bound by quite flat sternocostalia with the breast-bone, 

 with slender uncinate processess, each reaching to the next rib, 

 except on the two last. These latter are covered at their articu- 

 lation by the pelvis." 



I have attempted to construct from this description a formula to 

 compare with that of Heliornis, but I am not quite clear from the 

 description whether a free cervical rib is present and whether any of 

 the last ribs are lumbar. But apart from this it is clear that Podoa 

 difiers considerably from Podica, chiefly in the fact that there are no 

 rudimentary floating ribs behind the last, which is attached to the 

 sternum. The diff'erences indeed between Podica and Podoa in these 

 structures are (if the specimen studied by Giebel was not in any way 

 defective) if anything greater than the differences which distinguish 

 either genus from the Grebe or Coot. 



The following table indicates some points of comparison, as to 

 the number of vertebrae, ribs, &e., between Podica and some other 

 birds : — 



30* 



