90 



Asterospondyli . 



vided with an anterior spine. The Carboniferous shai-ks, 

 Spheuacanthiis and Trisfycldns, with cuspidate teeth and ribbed 

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

 fine teeth i'roni the Carboniferous Limestone named Orodns. 

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

 persistent notochord, cuspidate teeth, and ribbed dorsal fin- 

 spines (Fig. 12:^) ; many specimens, presumably males, are 



Fi0. 121. Fig. 123. 



Fig. 122. 



Fig. 121.— a, spine of Lepracanlhus Colei, Owen ; Coal-measures, Euabon, N. Wales ; 



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



Fig. 122. — Teeth of Acrodusf Anniv'iia, Ag. ; Lower Lias, Lyme Regis. 



Fig. 123. — Dorsal spine of Hyboilv.x ; 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 nnich 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 Myhodus exhibited, were obtained from the Lower Lias 



