Systematic Position of the Sheath-bills. 151 



outer surface of the head of this bone is distinctly grooved ; 

 in larine types it is flat and smooth. In this respect tlie 

 Sheath-bills are pluvialine, the Skuas larine. 



Pelvis. — The pelves of the Skuas and Gulls have easily 

 recognised characters, which serve to distinguish them from 

 other charadriiform types. For instance, the anterior iliac 

 fossee (on the dorsal surface of the ilia) are flattened and 

 much less hollowed out than in pluvialine types, while the 

 superior margins of these pre-acetabular portions of the ilia 

 are not continued dorsally into the characteristic prominent 

 hog's-back ridge which rides astride of the spinal processes 

 of the sacral vertebra in the Plovers and their kindred. 

 On the contrary, in tlie Skuas and Gulls this ridge has a 

 flattened and shaved-away apper.rance, and this is a very 

 characteristic feature. In these respects the pelves of the 

 Sheath-bills and Oyster-catchers are pluvialine. They are 

 also differentiated from the Gulls and Skuas in regard to 

 their incurved ischiadic processes, their more massive build, 

 and broader beam. The pelves of the Sheath-bills and 

 Oyster-catchers nevertheless present easily-recognised pecu- 

 liarities. Curiously enough, the pelves of the Skuas and 

 Gulls seem more generalised — that is to say, less specialised 

 away from the pluvialine type than either those of the 

 Chionididse or the Hgematopodidse. Thus in the sum of its 

 characters or general appearance the pelvis of Stercorarius 

 is very similar to that of Charadrius pluvialis. 



The Pelvic Limb. — I have no more to say here about this 

 than that in the Chionididse the hypotarsus of the tarso- 

 metatarsus is somewhat specialised and peculiar. In its 

 features it appears to stand somewhat by itself as compared 

 with adjacent groups. It is not larine. Charadrius even 

 seems more larine in respect of this part, or, to be more 

 correct, the Gulls are more pluvialine. It also differs from 

 Hamatopus, which again presents Gull-like propensities. 



A good many writers on the Sheath-bills have referred to 

 the resemblance that the legs and feet of these birds bear to 

 those of the Oyster-catcher. These resemblances are more 

 apparent than real, the bones of the pelvic limb being 



