E. LÖNNBERG, ON THE RHAMPHOTHECA OF BIRDS. 495 



The rhamphotheca of the upper jaw of the Gannet (Sula 

 bassana) is composed of the same pieces as that of the Cor- 

 morant, the only difference being that there are only two 

 upper labials both well defined as may be seen from the 

 figure. The lower jaw is more simple than in the Cormorant. 

 An unpaired narrow mentale is seen below in the symphyseal 

 tract, but the sides of the rami from the apex to the gape 

 are covered by only one shield on either side consisting no 

 donbt of two completely coalesced infralabials. 



In Fr egot a the npper jaw resembles that of the Cormo- 

 rant, bnt there is only one long labial shield fnlly developed, 

 the posterior region, which in the Cormorant is covered by 

 small labials, being in this bird less horny. The lower jaw 

 of the Frigate-bird has the same pieces as that of the Cor- 

 morant and they are also arranged in the same way, viz. 

 an unpaired mentale on the lower side of the apex, on either 

 side a short and strong first infralabial in the symphyseal 

 tract and a long second infralabial covering the ramus. 



The mentale is in some specimens very small and might 

 almost be termed rndimentary. Any proof that the long 

 posterior infralabial is composed of two are not offered but 

 an angular process of the feathered tract on the sides of the 

 mandible posteriorly might hint at that. 



The bill of the Pelecans (Pelecanus onocrotalus, rufescens, 

 fuscus etc.) is still more specialised and at the same time 

 simplified. The rhamphotheca of the upper jaw consists of 

 three well visible pieces. The median of these corresponds to 

 rostrale .+ internasale, and in some instances the distal end 

 of the latter may be traced wedged in into the former. The 

 lateral pieces correspond to one or more labials. The rham- 

 photheca of the lower jaw shows a median symphyseal suture 

 from which may be concluded that the mentale, already re- 

 duced in Fregata, here is wholly aborted. The rhamphotheca 

 of both halfs of the lower jaw is thus composed of the con- 

 fluent first and second infralabials, the first of them forming 

 the anterior compressed tip. 



JFrom a bill compound in the same way as that of the 

 Pelecans there is hardly even a step to such a one as that 

 found in Scopus. In this the rhamphotheca of the upper jaw 

 consists of three pieces: a median shield = rostrale + inter- 

 nasale, not conspicuously defined from each other, and a labial 



Arkiv för zoologi. Band 1. 36 



