E. LÖNNBERG, ON THE RHAMPHOTHECA OF BIRDS. 501 



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that the firm and powerful hook of the upper rhamphotheca 

 in the Falconiformes is formed, just as in Phalacrocorax, 

 Diomedea etc., by the rostrale alone and the härd covering 

 of the lower jaw by the mentale alone and all proximal parts 

 (intemasale, nasale, labialia, infralabialia &nåsubmandibularia) 

 have become reduced and form the cere. The situation of 

 the nostrils in the cere speaks for the correctness of such a 

 theory, because the surroundings of the nostrils which cor- 

 respond to nasalia is formed by cere, the median region 

 between the same = intemasale is cere and the labial tract 

 below the nostril at the börder of the inouth is also cere. 

 This transformation of the basal rhamphotheca holds even 

 steps with the shortening of the bill and stånds in casual 

 connection with the same, thus, as is already mentioned, the 

 »cere» of the comparatively longbilled Ynltures retains more 

 or less of its original horny character. 



According to this theory a rhamphotheca like that of 

 the Falconiformes might be directly derived from a bill which 

 has had snch a shape and generalised an ancestral structure 

 as that found in some Ciconiiformes namely the Cormorants, 

 Frigate-birds and allies. That is however as far as the upper 

 mandible is concerned and then simply by assuming a re- 

 duction of the elements so that the rostrale alone remains 

 and gets specialised. But if, as I presume, the lower rham- 

 photheca of the Falconiformes only consists of a highly de- 

 veloped mentale, such a condition cannot be directly derived 

 from such a one as that prevailing in the Cormorants be- 

 cause in the latter the mentale is on the way to be reduced 

 and is confined chiefly to the lower symphyseal tract instead 

 of being spread över the whole end of the mandible as in 

 the Falconiformes. 



The rhamphotheca of the Colymbi is said to be simple 

 in all books available to me. This seems, if it should be 

 true, the more peculiar as these birds are regarded as rather 

 primitive and allied to the extinct Ichthyornites. A close 

 examination of the upper rhamphotheca of a Diver makes 

 it, however, probable that it is composed of three diffe- 

 rent shields which have been fused together. This is espe- 

 cially distinguishable in specimens of Colymbus septentrio- 

 nalis from Greenland with the culmen of the bill whitish, 

 because then the different colour helps to discern the median 



