596 TROCEEDINGS OP THE GEOLOGICAL SOCIETY. [JunC 20, 



The accomiDanying sketch represents the crown (nat. size), which 

 probably shows a more advanced state of wear than any figured by 

 Cuvier*. 



The ear-bone is entire, and measures 1-4 inch in breadth, by 

 9 lines in vertical diameter. 



The specimens referred to in this note are in the Museum of the 

 Geological Society. 



11. On the Apeinities of Cb:on"Drostefs, Ag. 



By John Young, M.D., P.G.S. 



(This paper was withdrawn by permission of the Covnicil.) 



[Abstract.] 



The object of this communication was to show, from the characters of 



the skeleton, that Chondrosteus belongs not to the Chondrostean 



division of the ganoids as stated by Agassiz, but to the Holostean 



division, since it possesses a well-ossified basioccipital ; and the 



lateral walls of the cranium are composed of bones answering to the 



cartilage bones of ordinary Teleosteans. 



12. Notice of Few Geneka of Cabbonifeeous Glyptodipteeines. 

 By John Young, M.D., F.G.S. 



Since the publication, in 1861, of Professor Huxley's memoir on 

 the classification of Devonian Fishes, several new genera have been 

 established, and the intervals between some of the famihes (tabu- 

 lated at p. 24, Mem. Geol. Surv., Decade x.) thereby diminished. 



Rhizodopsis, Huxley. Eig. 8. 



The specimens to which this generic name has been given are 

 those whose scales Prof. Williamson described and figured in the 

 Phil. Trans. 1849, under the name of Hohptychms sauroides, a 

 term which has also been applied to a tooth which it will appear is 

 generically distinct from Holoptycliius. 



The body of this fish tapers to a point posteriorly ; its greatest 

 depth is at the pectoral arch. Head depressed ; orbits forward ; 

 gape wide, extending behind them. Maxilla in a single piece, fur- 

 nished with fine, equal, conical teeth ; premaxilla not preserved. 

 Mandible straight, deepest posteriorly, expanded at the symphysis ; 

 contains teeth of two sizes ; the larger, three or four in number, 

 plicate at the base, strong, conical, slightly incurved ; the smaller, 

 one-fourth of the size of the preceding, like them strong, conical : 

 the surface of all the teeth above the plicate base is smooth. Jugu- 

 lar plates in two pairs, principal and posterior. No trace of median 

 or lateral plates. The occipital region is closed in by three bones, 

 in front of which are the parietals in close approximation. The 

 facial bones are not determinable. Operculars large, subquadrate ; 

 suboperculars a half smaller, rounded anteriorly. The parietals, 

 operculars, and jugulars are ornamented with fine, parallel or bifur- 

 cating ridges. The facial bones and jaws have their surfaces reticu- 

 * Ossemen Fossiles, pi. xxxviii. figs. 9, 10, & 11. 



