_Haematopinus_, and very rarely is the same species found on different kinds of animals. The bird-lice (Mallophaga) are far more numerous in species, although the number of genera is comparatively small. With the exception of the genus _Trichodectes_, the various species of which are found on mammalia, all infest birds (as their English names implies) (see BIRD-LOUSE). Louse-infestation is known as phthiriasis in medical and veterinary terminology. AUTHORITIES.--The following works are the most important: Denny, _Monographia Anoplurorum Britanniae_ (London, 1843); Giebel, _Insecta Epizoa_ (which contains the working-up of Nitzsch's posthumous materials; Leipzig, 1874); van Beneden, _Animal Parasites_ (London, 1876); Piaget, _Les Pédiculines_ (Leiden, 1880); Mégnin, _Les Parasites et les maladies parasitaires_ (Paris, 1880); Neumann, _Parasites and Parasitic Diseases of Domesticated Animals_ (1892); Osborn, _Pediculi and Mallophaga affecting Man and the Lower Animals_ (Washington, 1891; U.S. Dept. Agr.); Enderlein, "Läuse-Studien," _Zool. Anz._ xxviii. (1904). LOUTH, a maritime county in the province of Leinster, Ireland, bounded N.E. by Carlingford Bay and Co. Down, E. by the Irish Sea, S.W. by Meath, and N.W. by Monaghan and Armagh. It is the smallest county in Ireland, its area being 202,731 acres or about 317 sq. m. The greater part of the surface is undulating, with occasionally lofty hills; in the north-east, on the borders of Carlingford Lough, there is a mountain range approaching 2000 ft. in height. Many of the hills are finely wooded, and towards the sea the scenery, in the more elevated districts, is strikingly picturesque. With the exception of the promontory of Clogher Head, which rises abruptly to a height of 180 ft., the coast is for the most part low and sandy. The narrow and picturesque Carlingford Lough is navigable beyond the limits of the county, and Carlingford and Greenore are well-known watering-places on the county Louth shore. The Bay of Dundalk stretches to the town of that name and affords convenient shelter. The principal rivers, the Fane, the Lagan, the Glyde and the Dee, flow eastwards. None of these is navigable, but the Boyne, which forms the southern boundary of the county, is navigable for large vessels as far as Drogheda.