1. History.—The genus Cladochonus was founded by Prof. M'Coy in 1847 (Annals Nat. Hist. vol. xx. p. 227) for certain Australian Palæozoic corals with “some relation to Aulopora,” but differing “in their curious erect habit, regular, angular mode of branching, slender, equal stem-like tubes, and abruptly dilated terminal cups bent in nearly opposite directions.”Prof. M'Coy also lays stress upon the thickness of the walls in Cladochonus, and the proportionately small calices, and states (loc. cit., and Ibid. 1849, vol. iii. p. 134) that the curious little corals formerly referred by him to Lamouroux's Jania will fall into this genus, viz. Jania crassa, and Jania bacillaria (Synop. Carb. Limestone Foss. Ireland, 1844, p.197). The Australian species Cladochonus tenuicollis is distinguished by the slenderness of the stolons connecting the calices. In 1851 Messrs. Milne-Edwards and Haime described a genus under the name of Pyrgia (Polyp. Foss. Terr. Pal. p. 310). which has been placed by subsequent writers as a synonym of Cladochnons, and we think with good reason. To their genus they assign the following characters—the corallum is free, pedicellate, with a strong epitheca, very deep calices, and without traces of septal striæ, and they consider that it differs from Aulopora in its simple and free habit. Two species were described, Pyrgia Michelini, Ed. and H., and P. Labechei, Ed. and H. The Janiæ of M'Coy they reserve their opinion on, but C. tenuicollis of the same authour is referred by them to the young of the genus Syringopora (loc. cit. p. 296). Similar views were expressed by them in their subsequent “Monograph of the British Fossil Corals” (pt. 3, Corals from the Perm. Form. and Mounatain Limset. p. 164). 1 and they further describe their Pygria Labechei (loc. cit. p. 166).