150 Mr. P. R. Lowe on the 



Gulls and Skuas this groove is deep and y-shaped, and very 

 characteristic. At the distal end of the humerus the depres- 

 sions for the braehialis muscle in the Slieath-bills and Skuas 

 are closely similar, being nothing like so deep as in the 

 Laridae. As regards the curvature of the shaft, the humerus 

 of the Sheath-bills is pluvialine ; that of the Skuas larine. 

 It may be here remarked that the sub-trochanteric fossa of 

 the Skuas is very markedly differentiated from that of the 

 Laridje, so that from this difference the bones of the two 

 forms could be recognised at a glance. In the Skuas, 

 a circular opening with smooth and well-defined margins 

 leads into a large pneumatic recess traversed by trabeculae, 

 and the tricipital fossa is inconspicuous. In the Laridae 

 the sub-trochanteric fossa is non-pneumatic, and a sharply- 

 defined riflge, curving inwardly, separates it from the 

 tricipital fossa. 



In this respect the humeri of the Sheath-bills, Hcema- 

 topus, and Dromas come closer to that of the Gulls than to 

 that of the Skuas. 



Phalanges. — The bony lateral expansion of the index digit 

 is not subdivided into two fenestrae (as in the Gulls and 

 Skuas) in either the Sheath-bills, the Oyster-catcher, the 

 Crab-Plover, or the Stone-Curlews. 



Sternum. — All that can here be said is that the general 

 morphology of the sterna of the Sheath-bills, the Oyster- 

 catchers, the Crab-Plover, the Skuas, and tlie Gulls presents 

 its own peculiar and characteristic features. Comparisons 

 seem quite futile. It is noticeable that in these sterna we 

 have a series of resultant evolutionary products, which have 

 been derived from a common ancestral type, or as the insult 

 of varying environmental or functional stresses. One 

 peculiarity, however, may be noted about the sternum of 

 the Sheath- bills, and that is that it entirely lacks the 

 diagonal pectoral ridge on the inferior surface of the body 

 of the sternum giving attachment to the outer border of the 

 pectoralis secundus, which ridge, so far as I am aware, is 

 present in all other Charadriiform types. 



Coracokl. — In pluvialine types I have noticed that the 



