Key to the Genera.
a. Bill narrow ; breadth at forehead not more than half length of culmen ; rictal bristles well developed. '. Sexes different in coloration. a". Axillaries and under wing-coverts in both sexes uniformly of one colour or very nearly so ; lower plumage never blue nor chestnut combined with black or blue MKBULA, p. 121. //'. Axillaries and under wing-coverts in both sexes of two colours in strong contrast ; arrangement of colours in axillavies transposed in under wing- coverts GEOCICHLA, p. 130 c". Axillaries and under wing-coverts in males of one colour, in females more or less barred with two colours ; lower plumage of males wholly blue, or chest- nut combined with blue or black, in females squamated.
a'". Tail very much longer than half wing PETBOPHILA, p. 142.
It" . Tail about equal to half wing MONTICOLA, p. 147. I'. Sexes alike in coloration. d' 1 . Axillaries and under wing-coverts en- tirely of one colour TURDUS, p. 148. e. Axillaries and tinder wing-coverts of two colours ; arrangement of colours in axillaries transposed in under wing- coverts. c'". Lower plumage distinctly barred or spotted ; rictal bristles few and lateral OREOCINCLA, p. 151. d'". Lower plumage squamated; rictal bristles numerous, and anterior ones projecting forwards over nostrils .... ZOOTHERA, p. 156. b. Bill broad ; breadth at forehead more than half length of culmen ; rictal bristles obsolete . . COCHOA, p. 158.
Genus MERULA, Leach, 1816.
I restrict this genus to those Thrushes in which the sexes are different in coloration and in which the under wing-coverts and axillaries in both sexes are uniformly of one colour or nearly so. The lower plumage of the Thrushes of this genus is, moreover, never blue, nor chestnut combined with black or blue.
In Met-ula the bill is about half the length of the head ; the rictal bristles moderate ; the wing long and sharp, the first primary being small ; the tail rather ample, and the tarsus long. The underside of the wing has no pattern.
