L. C. MIA.LL ON THE STRUCTURE OF THE SKULL OF BHIZODUS. 627 



the true relations of the genera, it is undesirable even to attempt to 

 rectify the nomenclature of the groups. 



A (acute-lobate). 



Ceratodus. Phaneropleuron. 



Lepidosiren. 



Holoptychius, 



Dipterus. Glyptolepis. 

 Ctenodus. 



B (obtuse-lobate). 



Megalichthys. Glyptopomus. 



Osteolepis. Gyroptychius. 



Diphpterus. 



Polypterus. 



Rhizodus. 



lihizodopsis. Coelacanthus. 



Undina. 



Glyptolcemus. Macropoma. 



It may be useful to future investigators if I enumerate the chief 

 writings which deal with Rhizodus. They are as follows : — 



Hibbert, " On the Limestone of Burdiehouse, Edinburgh," Trans. Roy. Soc. 



Edinburgh, vol. xiii. pt. i. pp. 202-214, t. viii. figs. 1, 2, t. ix. figs. 2, 3, 9, 10, 



t. x. figs. 1, 2, 3 (1835). 

 Owen, Odontography, p. 75, t. xxxv. fig. 2, tt. xxxvi., xxxvii. (1840-45). 

 Sedgwick and M ; Coy, British Palaeozoic Fossils, p. 611, 612, t. 30. fig. 17 



(1855). 

 Huxley, " Essay on the Systematic Arrangement of the Fishes of the Devonian 



Epoch," Mem. Geol. Survey, Decade x. (1861). 

 Young, " Note on the Scales of Rhizodus," Quart. Journ. G-eol. Soc. vol. xxii. 



p. 317 (1866). 

 Young. " Notices of new Genera of Carboniferous Grlyptodipterines," ib. p. 596 



(1866). 

 Hancock and Attmey, " Remains of Reptiles and Fishes from the Northumber- 

 land Coal-field," Nat. Hist. Trans. Northumberland and Durham, vol. iii. 



p. 81 (1869). 

 Traquair, " On some Fossil Fishes from the neighbourhood of Edinburgh," 



Ann. Nat. Hist. ser. 4, vol. xv. p. 258 (1875). 



The thanks of those who may be interested in this subject are due 

 to Prof. T. McKenny Hughes, M.A., the Woodwardian Professor of 

 Geology, Cambridge, by whose permission the skull of Rhizodus is 

 now described — and to Mr. Thomas Atthey, of Grosforth, Newcastle, 

 who cleared the specimen from the matrix, and developed its fea- 

 tures with much care and skill. 



