28 



PISCES 



CLASS I 



S. hybodoides, Egert. sp., represented by fin spines and teeth in English, 

 Welsh, and Scottish Coal Measures. 



Hybodus, Ag. (Meristodon, Ag.), (Fig. 51). Teeth and dorsal fin spines 

 almost as in Sphenacanthus ; but double series of denticles on hinder face of 



fin -spine median, not laterally placed. 

 Symphysial teeth few and relatively 

 large. Notochord persistent, but ver- 

 tebral arches calcified. One or two 

 large hook-shaped, semi-barbed dermal 

 spines (Sphenonchus) immediately behind 

 each orbit, at least in the male. Shagreen 

 sparse, consisting of small conical, 

 radiately grooved tubercles, which are 

 sometimes fused into groups of three. 

 Numerous species ranging from the Trias to the Lower Cretaceous. Teeth 

 of H plicatilis, Ag. (Fig. 51, A), abundant in the Muschelkalk. Nearly 

 complete skeletons from the Lower Lias of England (H delabechei, Charles- 

 worth ; H. reticulatus, Ag., Fig. 51, B) and the Upper Lias of Wurtemberg (H. 

 hauffianus, Eb. Fraas). Fine skulls from Wealden, Pevensey Bay, Sussex 

 (H basanus, Egert.). 



Acrodus, Ag. (Thectodus, Plieninger), (Fig. 52). A genus only differing 

 from Hybodus in the rounded, non-cuspidate character of the teeth. Common 



Fig. 51. 



Teeth of Hybodus. A, H. ■plicatilis, Ag. Muschel- 

 kalk ; Laineck, near Bayreuth. B, H. reticulatus, 

 Ag. Lower Lias ; Lyme Regis, Dorsetshire. C, H. 

 polyprion, Ag. Lower Oolite (Dogger) ; Stonestteld, 

 < ►xfordshire. 



Fig. 52. 



Acroda* anningiae, Ag. Dentition, 1/3 natural size. Lower Lias ; Lyme Regis. 

 A, .Symphysis. B, Detached tooth, seen from side and above, natural size. 



in the Triassic and Jurassic, and ranging to the Upper Cretaceous. A. 

 gaillardoti, Ag., teeth from Bunter, Muschelkalk, and Keuper of Germany 

 and France. A. minimus, Ag., common in European Keuper and Rhaetic. 

 A. anningiae, Ag. (Fig. 52), and A. nobilis, Ag., known by fine specimens from 

 the Lower Lias, Lyme Regis. A. levis, Sm. Woodw., teeth from English 

 Gault. 



Palaeobates, Meyer. Teeth depressed, rounded, without lateral denticles 

 and not keeled. European Triassic. 



Aster acanthus, Ag. (Strophodus, Ag. ; Curtodus, Sauvage), (Figs. 53, 54). 

 Principal teeth elongated, irregularly quadrate, with slightly arched but 

 flattened crown ; symphysial teeth few, smaller but relatively large, much 



