E. LÖNNBERG, ON THE RHAMPHOTHECA OF BIRDS. 491 



the mandible and covering the whole lateral surface of the 

 ramus as well. This shield makes the impression of being 

 quite simple but it is nevertheless composed of two shields 

 which have become so thoroughly fused together. These two 

 shields are situated longitudinally above each other and may 

 be termed as follows, the npper = a second infralabial, and 

 the lower a submandibular. x A longitudinal groove in front 

 indicates the division in two shields and in some species the 

 posterior division is marked as well, viz. by an angnlar strip 

 wedged in from the feathered tract basally between the 

 infralabial and submandibular elements. The fusion appears, 

 however, in most cases to be so complete that it wonld seem 

 daring to express such a view as that above if it was not 

 for the structural condition of the bill of other Tubinares 

 belonging to other families as will be seen below. I am also 

 snrely convinced that the ontogenetic development of the 

 Albatrosses shall prove the correctness of my opinion as to 

 the duplicity of this shield. 2 



In a specimen of Diomedea melanophrys the same struc- 

 ture as that now described was fonnd, but the first upper 

 labial was more reduced than in other specimens of this 

 genus which I have had the opportunity of examining. In 

 Thalassogeron culminatus the first labial is also much reduced 

 and very narrow. From this arrangement of the elements 

 of the compound rhamphotheca typical for the Albatrosses 

 that of other Tubinares differs through one or the other 

 modification. In the Fulmarine birds (and others), the nasal 

 tubes have become enlarged and coalesced on top of the 

 culmen. The median suture between both may, however, be 

 traced more or less plainly on top of the bill. Other modifi- 

 cations with regard to the nasal tubes are found in other 

 species but the original condition and the homologies are of 

 course not obscured by this. 



The first labial is much reduced in Ossifraga gigantea, 

 but may be easily recognised on the toothlike projection 

 derived from the same (conf. above). In youngs of Fulmarus 

 glacialis it is plainly visible all the way from the (pre-) 

 maxillary börder just behind the rostral hook to the anterior 



1 Conf. the condition described above from -»Ratitce» and Tinamiformes. 



2 Since the above already was printed I have had the opportunity of 

 state the correctness of this hypothesis. 



