70 Loological Society :— 
hardly elevated 0-2 inch above the general level, rises to an enormous 
size in P. Rippellii (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. 
\ \ ACNE 
‘N\ 
Fig. 2. 
Their conformation is otherwise generally similar, that of P. Riip- 
pellit being slightly narrower, and rather longer. It may be re- 
marked, however, that the skull of P. Riippelli 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. 
