90 



Aster ospondyli. 



vided with an anterior spine. The Carboniferous sharks, 

 Sphenacanthus and Tristychius, with cuspidate teeth and ribbed 

 dorsal fin-spines, are probably to be placed here ; so also are the 

 fine teeth from the Carboniferous Limestone named Orodus. 

 Hybodus, ranging from the Muschelkalk to the Wealden, has a 

 persistent notochord, cuspidate teeth, and ribbed dorsal fin- 

 spines (Fig. 123) ; many specimens, presumably males, are 



FIG. 121. 



FIG. 123. 



FIG. 122. 



FIG. 121. A, spine of Lepracanthus Colei, Owen ; Coal-measures, Ruabon, N. Wales ; 



B, a portion of the spine enlarged, to show tbe external ornamentation. 



FIG. 122. Teeth of Acrodus Anningicc, Ag. ; Lower Lias, Lyme Regis. 



FIG. 123. Dorsal spine of Hybodus ; Wealden, Sussex. 



further provided on either side of the head with two large 

 barbed booklets, each fixed on a broad base, and these were 

 originally named Sphenonchus by Agassiz. who supposed them to 

 be the teeth of a distinct fish. The skull much resembles that 

 of Notidanus, and the teeth in some species are also very similar 

 to the early forms of the last-named genus. The finest speci- 

 mens of Hybodus exhibited, were obtained from the Lower Lias 



