E. LÖNNBERG, ON THE RHAMPHOTHECA OF BIRDS. 



497 



tooth-like the tip of the lower jaw represents an unpaired 

 mentale, although it is not by sutures defined from the sides 

 which must correspond to infralabials. The theory concerning 

 the honiology of the tip of the lower rhamphotheca with a 

 mentale is based on the condition found in the young not 

 yet feathered Cancroma, in which a well defined mentale is 

 seen on the tip of the lower jaw. 1 It is not probable how- 

 ever, that the homologon of the mentale always in the Herons 

 is to be songht at that same place, at the extreme tip of the 

 lower jaw, becanse in other representatives of this family 

 (Tigrisoma and even in yonng specimens of Ardea cinerea) I 

 have fonnd what I regard as a rudiment of this plate in the 

 shape of a narrow strip-like piece wedged in between the 

 infralabial shields below and at the posterior end of their 

 symphysis. To jndge from this it might be possible that 

 in many of the typical Herons 

 the mentale has wholly disappeared 

 rather than that it has become fused 

 with other shields. The horny co- 

 vering of the rami mandibulares is 

 as a rule so uniform that it is diffi- 

 cnlt to say if it is a single shield 

 or several fused together into one. 

 In Tigrisoma there seems, however, 

 to be a division proximally between 

 an infralabial and a snbmandibular aKhough not very pro- 

 nonnced. The only hint otherwise of the latter possibility 

 is a small projection from the feathered tract which in some 

 herons protrudes a little on the sides of the lower jaw from 

 behind and might indicate a snbdivision into an infralabial 

 and a snbmandibular. This feathered point is, however, as a 

 rule only little developed and is not seen in Balceniceps, 

 Cancroma and many others in which the bill otherwise is 

 less specialised. 



The rhamphotheca of the Ibises exhibits a very great 

 resemblance to that of Scopus with regard to its composition. 

 The upper rhamphotheca is thus compound of three longi- 

 tudinal pieces, a median and one on either side, which all 

 of them are quite distinct from the base to the tip of the 



1 In the same the nasal or the covering of the nostril is quite distinct 

 from the median piece. 



Fig 7. The bill of a young, 

 not feathered Cancroma. 



