286 THE AMERICAN NATURALIST. | [Vor. XXXV. 
fortwo subprovinces. Here is shown a considerable separation 
of the means (indicated by the vertical line) for the subprovince 
polygons, indicating a larger bill for Austroriparian shrikes 
(5.8), which are also seen in Fig. 67 to have a greater depth 
of bill. The increase in size found in the bills of Florida 
shrikes is also shown by comparison of Tables IV and V, in 
which these characters are correlated for a series of Florida! 
shrikes and a series from the Appalachian subprovince. A 
striking absence of correlation and a great tendency towards 
individual variation in the proportions of the bill are to be seen. 
Increase in the relative size of the bill in many southern birds 
has been noted by Allen (71). It would be an interesting field 
for statistical investigation. 
TABLE IV. — 32 MALE SHRIKES FROM FLORIDA. 
Classes of Length of Bill in Millimeters. 
eT of Total. 
epth of Bill. 
H3] In5 | 119 | tat | 13234 | 12 1.330] 1333] 15:6 | $35 
8.8 mm | 1 I 2 
9.0 mm. I I 2 
9.2 mm. 2 I I I 5 
9.4 mm. I I I 3 
9.6 mm. 2 2 
9.8 mm. I I I I 2 6 
10.0 mm. I 5 i 4 I1 
10.2 mm. I : 
Total 3 10 4 3 7 4 I 32 
3. Color.— Frequency polygons for variations in the melan- 
ism of the head are shown in Fig. 7. The upper polygon (Fig. 
7A), which includes the entire series, is seen to be distinctly 
bimodal, and in the lower polygons we see that the mode of 
greater melanism is due to the presence of Austroriparian 
shrikes, and that the shrikes of the Campestrian subprovince 
have the least melanism for the dorsal surface of the head. 
1 Only Florida representatives of the Austroriparian shrikes were taken in this 
case, in order to eliminate intermediate forms, for it seemed desirable to me to 
compare the Appalachian shrikes with a group as nearly tropical as possible. 
