MILLERITE  , a

mineral consisting of nickel sulphide, NiS . Crystals belong to the rhombohedral system and have the form of slender needles arranged in divergent groups or of delicate fibres loosely matted together . The colour is brass-yellow and the lustre metallic . Before the chemical composition of the mineral had been determined it had been known as " capillary pyrites " or " hair pyrites " (Ger., Haarkies), and was not distinguished from the capillary forms of pyrites and marcasite: the name millerite was given by W . Haidinger in 1845, in honour of W . H . Miller . The hardness is 3–31 and the specific gravity 5.65 . There are perfect cleavages parallel to the faces of the rhombohedron (too); and gliding planes parallel to the faces of the rhombohedron (11o), on which secondary twinning may be readily produced artificially by pressure . Typical specimens of millerite are found in the coal measures in the neighbourhood of Merthyr Tydvil in South Wales, where the delicate needles and fibres occur with crystals of quartz and pearl-spar in the fissures of septarian nodules of clay-ironstone . Radiating groups of needles are found with ankerite in cavities in haematite in the Sterling. mine at Antwerp in Jefferson county, New York . At the Gap mine in Lancaster county, Pennsylvania, the mineral occurs as fibrous encrusting masses with a velvety lustre .

The most perfect crystals are those formerly found with

calcite, diopside and a bright green chrome-garnet in a nickel mine at Orford in Sherbrooke county, Quebec . (L . J . S.) MILLER'S THUMB (Coitus gobio), a small fish, abundant in all rivers and lakes of northern and central Europe with clear water and gravelly bottom . The genus Coitus, to which the miller's thumb belongs, is easily recognized by its broad, flat head, rounded and scaleless body, large pectoral and narrow ventral fins, with two dorsal fins, the anterior shorter than the posterior; the praeoperculum is armed with a simple or branched spine . The species of the genus Coitus are rather numerous, and are confined to the north temperate zone of the globe, the majority being marine, and known by the name of " bullheads." The miller's thumb is confined to fresh water; and only one other freshwater species is found in Europe, C. poecilopus, from rivers of Hungary, Galicia, and the Pyrenees; some others occur in the fresh waters of northern Asia and North America . The miller's thumb is common in all suitable localities in Great Britain, but is extremely rare in Ireland; in the Alps it reaches to an altitude exceeding 7000 ft . Its usual length is from 3 to 5 in . Generally hidden under a stone or in a hollow of the bank, it watches for its prey, which consists of small aquatic animals, and darts when disturbed with extra-ordinary rapidity to some other place of refuge . The female deposits her ova in a cavity under a stone, whilst the male watches and defends them until the young are hatched and able to shift for themselves .