DELPIIINUS DELPIIIS. 



47 



We learu from this table that, in a general way, the beak is propor 

 tionally longest in the largest, most nearly adult, skull; also that the 

 proportion of the width of the beak to its length is not co-ordinated- 

 with the absolute size of the skull. The longest beaks are not always 

 the narrowest. 



The shortest beak in this series of females is in length 54.7 per cent, 

 of the total ; the longest, Gl.l per cent. The widest beak has a breadth 

 equaling 22.5 per cent, of its length, and the narrowest 17.3 per cent. 

 The average length of the beaks for the three largest skulls is G0.5 

 per cent. ; for the whole series, 58.3. The average width of the three 

 largest is 19.3 per cent. ; for the whole series, 20.1. 



M. Fischer gives measurements of only two males. The proportions 

 of the beak in these and one additional male in the national collection 

 are shown in the following table: 



In these three specimens again we find that there is no correlation 

 between the width of the beak and the absolute size. 



The length of the longest beak is G2.5 per cent, of the total, or a little 

 more than that of the longest-beaked female. The average proportional 

 length of the beak is also a little more than in the three largest females, 

 viz, Gl.l per cent. The widest beak has a breadth equaling20.1per cent, 

 of its absolute length, and the narrowest IG.G per cent. The latter pro- 

 portion is considerably less tban in the females, while the average, 18.3 

 per cent, is also less. 



M. Fischer's generalization is borne out by these percentages, but it 

 should be remembered that two of the three males here considered are 

 absolutely larger than any of the females. Since the iiercentage of the 

 length of the beak rises with the absolute size of the skulls, if the females 

 reach the same size as the males, it appears to me probable that males 

 and females of the same absolute size would give the same percentages 

 of leugth of beak. This opinion receives some support from the fact 

 that M. Fischer's male "fusus D," which is absolutely larger than any 

 of the females except '■^fusus B," has a relatively shorter beak than three 

 of the females. 



In addition to the individuals already discussed, I have myself meas- 

 ured a considerable number of similar skulls in the Museum d'Histoire 

 Naturelle, the British Museum, aud elsewhere. In many cases the 

 localities are not given. 



