Prince C. L. Bonaparte,[328] a great divider of species, enumerates, with a mark of interrogation, as distinct from _C. livia_, the _C. turricola_ of Italy, the _C. rupestris_ of Daouria, and the _C. Schimperi_ of Abyssinia; but these birds differ from _C. livia_ in characters of the most trifling value. In the British Museum there is a chequered pigeon, probably the _C. Schimperi_ of Bonaparte, from Abyssinia. To these may be added the _C. gymnocyclus_ of G. R. Gray from W. Africa, which is slightly more distinct, and has rather more naked skin round the eyes than the rock-pigeon; but from information given me by Dr. Daniell, it is doubtful whether this is a wild bird, for dovecot-pigeons (which I have examined) are kept on the coast of Guinea. The wild rock-pigeon of India _(C. intermedia_ of Strickland) has been more generally accepted as a distinct species. It chiefly differs in the croup being blue instead of snow-white; but as Mr. Blyth informs me, the tint varies, being sometimes albescent. When this form is domesticated chequered birds appear, just as occurs in Europe with the truly wild _C. livia_. Moreover we shall immediately have proof that the blue and white croup is a highly variable character; and Bechstein[329] asserts that with dovecot-pigeons in Germany this is the most variable of all the characters of the plumage. Hence it may be concluded that _C. intermedia_ cannot be ranked as specifically distinct from _C. livia_. In Madeira there is a rock-pigeon which a few ornithologists have suspected to be distinct from _C. livia_. I have examined numerous specimens collected by Mr. E. V. Harcourt and Mr. Mason. They are rather smaller than the rock-pigeon from the Shetland Islands, and their beaks are plainly thinner; but the thickness of the beak varied in the several specimens. In plumage there is remarkable diversity; some specimens are identical in every feather (I speak after actual comparison) with the rock-pigeon of the Shetland Islands; others are chequered, like _C. affinis_ from the cliffs of England, but generally to a greater degree, being almost black over the whole back; others are identical with the so-called _C. intermedia_ of India in the degree of blueness of the croup; whilst others have this part very pale or very dark blue, and are likewise chequered. So much variability raises a strong suspicion that these birds are domestic pigeons which have become feral. {185}