70 



Zoological Society : — 



hardly elevated 0-2 inch above the general level, rises to an enormous 

 size in P. Riippellii (fig. 2), attaining a height of 1*05, a breadth of 

 0*75, and a length from back to front of 1*65. It may also be re- 

 marked that, from the hard character of the osseous structure in 

 the protuberance of P. gambensis, it is obvious that it has reached 

 its maximum of development. The outlines of the two skulls are 

 represented in the accompanying woodcuts. 



Fig. 



Fig. 2. 



Their conformation is otherwise generally similar, that of P. Riip- 

 pellii being slightly narrower, and rather longer. It may be re- 

 marked, however, that the skull of P. Riippellii is broader between 

 the orbits ; but that, drawing a vertical line from the middle of the 

 space between the nostrils to a base-line joining the edges of the upper 

 mandibles, and comparing them at this point, it is here narrower and 

 more elevated, — the proportion of the vertical to the base being in P. 

 Riippellii about 3 : 5, in P. gambensis about 7:9. The depressed 

 space between the protuberance and the naked part of the bill is also 

 somewhat differently shaped in the two birds. In P. Riippellii the 

 outline of this space next to the protuberance forms a segment of a 

 circle of which the centre is at the junction-point of the two other 

 sides, so that the space enclosed is nearly a quadrant. In P. gam- 

 bensis the corresponding outline is carried back much further towards 

 the protuberance, and formed of two lines, which terminate in a cen- 

 tral angle, so that the space enclosed is nearly a rhombus. 



