Crossopterygii. 



99 



scales and obtusely-lobate paired fins. RJiizodopsis is represented 

 by small species in the Carboniferous, Rhizodus and Strepsodus 

 by comparatively large species. A fine series of remains of 

 Rhizodus Hibberti and R. ornatus, from the Lower Carboniferous 

 of Scotland, is exhibited in Wall-case No. 6. 



Wall- case 

 No. 6, 



FIG. 139. Osteolepis macrolepidotus, Ag. (restored by C. II .Pander) ; L, Old Red 

 sandstone, Scotland. 



No. 35. 



The Ccelacamthidae (hollow-spines) are the most remarkable Wall-case, 

 Crossopterygians, ranging almost unchanged from the Lower 

 Devonian to the Upper Chalk. Their name refers to the cir- 

 cumstance that the spines of the backbone are only superficially 

 ossified and so appear hollow when fossilized. The head-bones 

 and opercular bones are much reduced, and the tail is produced 

 into a small terminal extension. The air-bladder is ossified. 

 The trunk is covered with thin, deeply overlapping scales. 



FIG. UQ.Undina (HolopJtagu*) rjulo, Egert. ; L?wer Lias, Lyme Regis. 



Ccelacanthus is Carboniferous and Permian ; Undina (Fig. 140) 

 is Jurassic, and beautiful specimens are exhibited from the 

 Lower Lias of Lyme Regis ; Macropoma is Cretaceous, and 

 represented by the unique collection of Dr. Mantell besides 

 later acquisitions from the English Chalk. 



8 2 



-, 



*r V t TT tt t! 



