Mr. P. R. Lowe on the Crab-Plover. 327 



The most noticeable feature, however, of the cranial roof 

 is the well-marked supraorbital depressions, which are 

 remarkable for their resemblance to those of Lams. The 

 depressions or grooves meet in the mid-line of the interorbital 

 region, a tliiu sagittal ridge of bone alone separating them 

 (c/*. text-figure 10). 



As in Larus, the floor of either groove is perforated 

 towards the hinder margin of the orbital rim by small 

 foramina or fenestra. In the Skuas and Sheath-bills there 

 is a distinct break in the continuity of the curve of the outer 

 edge of the orbital rims in this region, while the fenestra in 

 the floor of the grooves are larger, so that in this respect 

 the Skuas differ from either Larus or Dramas. 



As compared with Larus, the interorbital space in Dramas 

 is more elongated, but otherwise there are no essential 

 differences, and we may even observe in the two forms a 

 faithful reproduction of the curious ear-shaped processes of 

 bone in which the orbital margins of either side terminate 

 as they approach the postorbital processes. In the form and 

 structural details of this interorbital region Hamatopus is, of 

 course, also notoriously larine — that is to say, it is similar 

 in this respect to Larus canus. 



Lacrymals. — Still proceeding forwards, we arrive at the 

 lacrymals, and here, for the first time, we note any very 

 obvious morphological differences between the skulls of 

 Dromas and Larus. 



In Larus the orbital portion of the lacrymal is produced 

 outwards and backwards as a free and prominent process 

 (cf. text-figure 10). In Dromas the orbital portion of the 

 lacrymal has no such free process. On the contrary, it is at 

 first directed abruptly outwards at right angles to the long 

 axis of the skull, and then again makes a right-angled turn 

 forwards and downwards, to be continued into the descending 

 process of the lacrymal. In this respect Dromas is pluvialine. 



As regards the descending process of the lacrymal in the 

 two forms, there are certain noticeable diff"erences. In both 

 Larus and Dromas it is first continued downwards, forwards, 

 and slightly inwards, and then is bent backwards so as to 



