E. LÖNNBERG, ON THE RHAMPHOTHECA OF BIRDS. 487 



The condition of the rhamphotheca of the Tinamous resem- 

 bles very nmch that of the »Batitce». In a specimen of Crypturus 

 I find an unpaired median piece on the upper jaw correspond- 

 ing to rostrale and on either side a piece corresponding to 

 labialia. The base of the upper jaw is covered by an appar- 

 ently somewhat softer layer in the same place as and similar 

 to the internasal of the Ostrich. The lower jaw exhibits a quite 

 typical and sharply limited mentale of longish triangulär shape 

 with the pointed end at the proximal side of the symphysis. 

 On either ramus of the mandible the upper edge is formed 

 by a longitudinal infralabial plate and the lower side is 

 protected by a submandibular shield which especially pöste - 

 riorly, is well separated from the foregoing and extends rather 

 far back. In Nothura media the same parts are to be found, 

 but the mentale of the lower jaw is not triangulär but rec- 

 tangular having a square proximal end. The bill of these 

 birds cannot be said to be much specialised. 

 But in Bhynchotus rufescens the compara- 

 tively long and strong bill shows a higher 

 degree of specialisation. This is no doubt „. 1 T , . 

 due to the fact that the bill of this bird rhamphotheca of 

 is subiected to being more worn at its Crypturus seen 



J m -i • t from below. 



extremity when the bird grazes, and that 

 so is the case may easily be seen on an adult bird of this 

 species, for its bill gives the impression of being strongly 

 worn as well as rapidly growing. In consequence hereof the 

 different elements of the upper rhamphotheca are more den- 

 sely fused together. Nevertheless, an unpaired median and 

 a lateral shield on each side may be discerned separated by 

 longitudinal furrows which become less conspicuous towards 

 the tip. The basal portion resembles that of Nothura although 

 there are distinct indications of a stronger basal growth 

 which on the sides in some specimens look like a separate 

 posterior labial although less well defined. The lower jaw of 

 Bhynchotus shows the remarkable difference that the mentale 

 is quite reduced and absent so that both infralabial shields 

 meet along a median suture which extends quite plainly to 

 the worn tip. This is of interest because the same kind of 

 transformation is to be met with in other groups of birds. 

 In Bhynchotus this reduction is a result of the wearing in- 

 fluence on the bill effected when the birds are grazing or 



