153. GREAT NORTHERN DIVER. _Colymbus glacialis_, Linnaeus. French, "Plongeon imbrim."--The Great Northern Diver is a common autumn and winter visitant to all the Islands, arriving early in November, perhaps even about the last week in October. The earliest date at which I have seen it myself was on the 9th November. A considerable majority of these autumnal visitants are young birds of the year, the rest being adults in winter plumage; but, as is the case on the south coast of Devon, a few occasionally remain so late on in the spring as to have fully attained the breeding-plumage. There is one Guernsey-killed specimen in perfect, or nearly perfect, breeding-plumage in the Museum, which I think was killed some time in May by Mr. Peter Le Newry, a well-known fisherman and gunner living in Guernsey, who procured a good many specimens for that establishment, but, unluckily, no note as to date or locality has been preserved; he told me he had killed this bird late in the spring, but could not when I saw him remember the exact date. It must not be supposed that because this bird occasionally remains in the Islands late into the spring, and assumes its full breeding-plumage before leaving, that it ever remains to breed or avails itself of the protection so kindly afforded to it and its congeners, as well as their eggs, by the Guernsey Bird Act. The Great Northern Diver is included in Professor Ansted's list, but only marked as occurring in Guernsey. There are four specimens in the Museum in full breeding plumage and change. 154. BLACK-THROATED DIVER. _Colymbus arcticus_, Linnaeus. French, "Plongeon à gorge noir."--The Black-throated Diver is a much less common visitor to the Islands than either the Great Northern or Red-throated Diver; it does, however, occasionally occur in the autumn and winter; all the specimens that have been obtained are either immature or in winter plumage, and I do not know of a single instance in which it has been procured in full plumage as the Great Northern has. In the 'Zoologist' for 1875 Mr. Couch records the occurrence of a Black-throated Diver on the 19th of January of that year, and of another on the 30th of the same month; these are the most recent occurrences of which I am aware. No doubt the young Black-throated Diver may be occasionally mistaken for and passed over as the young Northern Diver; but it may always be known by its much smaller size, being intermediate between that bird and the Red-throated Diver, from which, however, it may always be distinguished by wanting the white spots on the back and wing-coverts which are always present in the winter plumage of the adult Red-throated Diver, and the oval marks on the margins of the feathers of the same parts in the young birds of the year. The Black-throated Diver is included in Professor Ansted's list, and marked as only occurring in Guernsey. There is one specimen, an immature bird, in the Museum.