332 j\rr. P. U. Lowe on the Crab-Pluver. 



Charadriiform groups with which Ave have compared them ; 

 but of these genera they are closest to Oi'thorhomphus. The 

 resemblance to Orthorhamphus is remarkable, but is probably 

 an instance o£ parallelism^ or due to similar functional stresses. 

 The resemblance of the interpalatine laminae and the pre- 

 palatine processes with tlieir continuation forwards into the 

 palatal processes of the premaxillse is to be specially noted. 



In Dromas the identity of the palatal surfaces of tlie 

 maxillo-palatines is almost lost on the prepalatine bars, 

 owing to their narrowness and to their nearly complete 

 fusion with these structures. In Orthorhamphus tlie fusion 

 is not so complete, but, nevertheless, the maxillo-palatines of 

 this genus come very close to those of Dromas. In Hamatopus 

 we seem, as regards the morphology of the palatal plates, 

 palatal bars, the complete fusion of the maxillo-palatines, 

 and their diminished size, to have gone a stage further than 

 Dromas. 



Reverting to the maxillo-palatines, these in Dy-omas 

 present on their external aspect and towards their hinder 

 half a slipper-like sac, with its toe directed proximal ly. 

 The maxillary sends a triangular process directly inwards to 

 join the maxillo-palatine at the point of entrance to this 

 slipper-like sac. In Ckionarchus I have noticed exactly the 

 same condition of things. In Orthorhamphus the maxillary 

 sends a like process inwards to fuse with the outer edge of 

 the scroll-like palatal surface of the maxillo-palatines. In 

 Hamatopus a modified or very specialised arrangement is 

 seen. In this last genus it is curious to notice that the 

 hinder border of the maxillo-palatines completely fuses with 

 the ethmoidal portion of the palatal plate, so that there is 

 absolutely no break whatever between the two. 



In Lams and Rissa the palatal surfaces of the maxillo- 

 palatines are quite free, except at their distal extremity 

 {cf. 'Ibis,' 1916, p. 146, text-figure 4), and here the 

 maxillary joins them. As a consequence, we get no fenes- 

 trum distad of this process in the Laridae, as we do in the 

 Skuas, Stone-Plovers, Oyster-catchers, Sheath-bills, Crab- 

 Plovers, and pluvialine forms generally. The difference in 



