496 



ARKIV FÖR ZOOLOGI. BAND 1. 



shield on either side. The lower jaw has, as it seems, a con- 

 tinous infralabial shield on either side. These meet anteriorly 

 along a median symphyseal suture which extends to the 

 extreme tip of the mandible. It is thus evident' that the 

 mentale has completely disappeared. But, to jndge from 

 some specimens at least, it seems probable that the infralabial 

 shield of either side in Scopus is composed of a smaller 

 anterior and a larger posterior infralabial which have com- 

 pletely coalesced. If this is right, as I believe, the bill of 

 Scopus agrees qnite nearly with that of Pelecanus and both 

 may easily be derived from a somewhat more primitive type, 

 for instance like that fonnd in Fregata. 



Fig. 6. The bill of Scopus from below and from the side. 



The npper rhamphotheca of the bill of Ard eid <s tcont&ms 

 evidently the same elements as that of Scopus, but the fusion 

 of the different pieces has in most cases gone further than 

 in the latter. In Balceniceps, however, the median piece of 

 the upper jaw is distinct. In Cancroma and many Herons, 

 especially young ones, the median piece of the upper rham- 

 photheca is well dehned from the lateral parts. But, on 

 the other hand, the fusion of the different element is in many 

 cases quite, complete, especially in Herons with slender bilis, 

 although even in such the suture is visible beyond the nasal 

 groove. The analysis of the lower rhamphotheca of these 

 birds is much more difficult. Not even in the Cancroma 

 when it is adult any sutures may be seen on the lower 

 rhamphotheca. It seems, however, probable that the terminal 



