THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE II. VOL. VI. 



No. VII.— JULY, 1879. 



ozRia-izrsr^.iiL articles. 



I. — On the Microscopic Structure op Three Species of the 

 Genus Cladochonus, M'Coy. 



By Prof. H. A. Nicholson, M.D., D.Sc, F.B.S.E., etc. ; 



and E. Etheridge, Jun., F.G.S. 



(PLATE VII.) 



1. History. — The genus Cladochonus was founded by Prof. M'Coy 

 in 1847 (Annals Nat. Hist. vol. xx. p. 227) for certain Australian 

 Palaeozoic corals, with " some relation to Aidopora," 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 propor- 

 tionately 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 Cladochonus, 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 strise, 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 Janice of M'Coy they reserve their opinion 

 on, but C. tenuicollis of the same author 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 

 Mountain Limest. p. 164), x and they further describe their Pyrgia 

 Labechei (loc. cit. p. 166). In 1849 Prof. M'Coy added to the 

 species of Cladochonus by the description of a form from the 

 Carboniferous Limestone of Derbyshire as C. brevicollis (Annals 

 Nat. Hist. 1849, vol. iii. p. 128), which possesses a peculiar zigzag 

 1 See also Hist. Nat. Corall. 1860, vol. iii. pp. 298 and 322. 



DECADE II.— VOL. VI. NO. VII. -19 



