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160 BRITISH PALAEOZOIC FOSSILS. [Crustacea. very obtusely rounded, width rather more than twice the length, of three tumid lobes, the axis most convex and rather more than half the width of the side lobes, with eight strong rounded segments, lateral lobes with a narrow entire margin and seven strong rounded ridges, the first one or two of which shew a very fine mesial dividing line; length five lines. Position and Locality.—Caradoc sandstone, Alt yr Anker, Meifod, Montgomeryshire; impure limestone of Capel Garmon, on the Cowney River, Denbighshire; Wilfa, near Penmachno; Pont y Glyn, Diffvvys, near Corwen ; Cwm of the Cymmerig, Bala, Merionethshire. Explanation of Figures.—PI. 1. G. fig. 12. Cephalic shield, natural size, (angles not perfect in specimen), from Capel Garmon.—Fig. 13 and 14. Pygidium natural size, from Pont y Glyn, Diffwys. Piiacops Downingiau (Murch. Sp.) Syn. and Ref—Galymene Id. Murch. Sil. Syst. t. 14. f. 3. Sp. Oh.—Ovate, depressed, head and pygidium of equal length; cephalic shield rotundato-trigonal, flattened, slightly more than twice as wide as long, margin obtusely angulated in front, (? lateral angles rounded); glabella very minutely and obscurely granulated, clavate depressed, anterior segmental furrows slightly sigmoid, oblique, second and third pair nearly transverse, all the furrows narrow and nearly reaching to the middle, the spaces behind the first pair are triangular, and broader than long, the second pair are transversely oblong, the space behind the third pair forms a nearly perfect transverse segment, only half as thick as the second space, or two-thirds that of the neck-furrow, which is very strong and prominent; first seven rings of the thorax equal to the length of the head; pygidium semi-oval, length more than half the width, axis prominent, of seven thick segments, sides with five flattened duplex segments. Length one inch two lines. Neither the figures in the “ Silurian System,” nor the “ Memoirs of the Geol. Survey,” exhibit the intermediary or duplicating furrows on the lateral ribs of the pygidium, they however may be seen to exist. Position and Locality.—Wenlock limestone of Dudley; Upper Ludlow of Benson Knot, Kendal; Moel Sessiog, Llanrwst. Sub-genus. Odontociiile (.If aide and Corda.) Syn. = Dalmannia Emmerich, (not of Robineau-Desvoidy). Gen. Char.—General form, buckler, glabella, eyes and eye-lines, as in Piiacops, but the lateral lobes of the glabella more equal; not contractile; thorax of eleven segments; pleuripedes curved backwards and generally pointed at their extremities, facets very long, narrow rhomboidal, slightly defined; pleural groove strong, slightly sigmoid and oblique (not angulated) ; pygidium elongate, generally pointed, axis with from twelve to twenty-two segmental furrows, sides with fewer (about half the number) strong ribs, usually duplex, confluent at their ends with the thickened entire margin; hypostoma with a dentate edge. This genus was first noticed by Emmerich under the name Dalmannia, w T hich w r as used fifteen years before for a genus of insects by Robineau-Desvoidy, I therefore use the name of Hawle and Corda, who do not allude to Emmerich’s having previously characterised the genus. Odontociiile caudata (Brong. Sp.) Ref. and Syn.—Asaphus caudatus Brong. Crus. Foss. t. 2. f. 4, and Murch. Sil. Syst. t. 7. f. 8. Sp. Ch.—Ovate, cephalic shield depressed, semi-ovate, twice as wide as long, exclusive of the lateral spines, which extend backwards and a little outwards as far as the sixth or seventh segment, confluent at base with the thick strongly defined borders of the circumference and posterior margin; glabella broadly clavate, slightly angulated in front, coarsely and irregularly granulated, the anterior pair of segmental furrows broad, and inclining obliquely backwards and inwards, the two posterior pair much narrower and nearly transverse; eyes very large conico-reniform; axal segments of the thorax four-fifths the width of