Linn., Syst. Nat, 10th ed., p. 16S (1758).
Type, Turdus merula Selby, 1835. Type-locality: Sweden.
The name Merula which has been used for the Thrushes and Blackbirds is pre occupied and therefore cannot be used, but even if it were not Linnaeus' name of Tardus would have priority. Linnaeus included a number of birds in the genus but the type was designated by Selby in 1835 as Tardus merula.
The genus contains those Thrushes of which the sexes are different in coloration and in which the under wing-coverts and axillaries in both sexes are either uniformly of one colour or very nearly so. The lower plumage of the Thrushes of this genus is, moreover, never blue, nor chestnut combined with black or blue.
In Turdus the bill is about half the length of the head; the rictal bristles are moderate; the wing is long and pointed and the first primary small; the tail is rather ample but varies considerably in comparative length ; the tarsus is stout and long and the underside of the wing has no pattern.
Key to Species.
A. General character of plumage black or dark brownish black.
a. Wings practically uniform blackish .. T merula, p. 123.
b. Wings with bold patch of light grey or
rufous-grey T. boulboul, p. 130.
B. General colour of plumage neither black nor very dark brown.
c. Hind neck of different colour to back,. T. castaneus, p. 132.
d. Hind neck of same colour as back.
a1. Whole head, neck and breast black . T. kessleri, p. 134.
b1. Whole head, neck and breast not black.
a2. Feathers of upper plumage varie¬gated with dark central streaks…T. eunomus, p. 133.
b2. feathers of upper plumage not variegated.
a3. Tail, throat and upper breast
chiefly chestnut T. ruficollis, p. 136.
b3. Tail, throat and upper breast not chestnut.
a4. Under wing-coverts and axil¬laries wholly or in part chestnut or orange-brown.
a5. Sides of breast and abdomen grey or brown.
a6. Throat and breast uni¬form.
a7. Throat and breast black T. atrogularis, p. 137. Throat and breast slaty-grey T. unicolor, p. 138.
b6. Throat and breast streaked.
c7. Under wing-coverts orange-brown ; axillaries rufous-grey .. T. atrogularis, p. 138. d7. Under wing-coverts and axillaries uniform chestnut-brown. T. unicolor, p. 139. b5. Sides of head and abdomen orange-rufous…………..T. dissimilis, p. 140.
b4 Under wing-coverts and axil¬laries slaty-grey.
c3 Breast and sides of abdo¬men chestnut-brown........ T. obscurus, p. 141.
d3. Breast and abdomen slaty-grey……………………….T. feae, p. 143.
c4. Under wing-coverts and axillaries pearl grey………T. pallidus, p. 135.