ON THE OYSTERCATCHERS. 43 
hexagonal reticulations. To this group belong ulso the Red- 
billed Curlew (Ibidorhynchus), the Stone Curlews (Cédicnemus), 
the Stilts and Avocets (Himantopus), and some of the Plovers 
Charadrius). To distinguish the genus Hematopus from these 
genera it is necessary to take into consideration two other 
characters. Compared with the Stilts, Stone Curlews, and 
Plovers, the Oystercatchers have long bills and short legs, so 
that the character of bill longer than tarsus effectually excludes 
these birds. It does not, however, exclude some of the Avocets, 
with their slender recurved bills, or the Red-billed Curlew, with 
a bill decurved like that of an Ibis. The clumsy, nearly straight 
bill of the Oystercatchers distinguishes them from these birds. 
In spite, however, of the extraordinary fact that it possesses a 
bill of such a totally different shape from that of an Oyster- 
catcher, there can be no doubt that the Red-billed Curlew is the 
nearest surviving relative of the Oystercatchers. It is, in fact, 
nothing but an Oystercatcher with a modified bill. The bill of 
the Oystercatchers is very abnormal. Most birds have beautiful 
bills remarkable for the subtlety of their curves, but the bill of 
the Oystercatchers can only be regarded by an artist as “sadly 
out of drawing.” The diagnosis of the genus Hematopus will 
therefore stand as follows:— 
Charadrude, with a nearly straight bill} longer than the 
tarsus, which is reticulated all round. Each of these three 
characters may be found in other birds of this family, but no 
birds belonging to it combine all three characters, except the 
Oystercatchers. 
There is abundant evidence in support of the hypothesis that 
the centre of dispersion of the Charadriide was the North Pole; 
that the Oystercatchers were originally residents on the shores of 
the Polar Sea, whence they were dispersed and driven southwards 
by the arctic ice which formed and reformed during the Glacial 
Epoch. Isolated on various distant shores, the consequences of 
isolation soon appeared and differentiated the Oystercatchers into 
several specific and subspecific forms. It is very interesting to 
trace their wanderings and to note their specific differences, which 
agree in a remarkable manner with the hypothesis of their polar 
origin and with their present geographical distribution, although 
the latter bears no sort of relation with the geographical regions 
laid down by Messrs. Sclater and Wallace, which refer to pas- 
