8 



Fossil Fishes. 



Table-case, 

 No. 27. 



Wall-case, 

 No. 2. 



Table-cases, 

 Nos. 27, 28. 



other forms, is discovered in a beautiful state of preservation in the 

 Upper Cretaceous of Mount Lebanon. 



The Notidayiidm are an ancient family, represented by four or 

 five species at the present day, and noteworthy both on account of 

 the primitive character of their skull (Fig. 17), and for the possession 

 of six or seven gill-clefts instead of the usual five. Teeth possibly 

 referable to Notidanus itself have been recorded from the Lias, 

 and several undoubted examples are known from the Oolites, 

 in addition to complete fishes from the Lithographic Stone of 

 Bavaria. The Chalk and Tertiary formations also yield numerous 

 species, and it is noteworthy that the largest and most complete 

 teeth are those of the latest deposits (Fig. 16). 



Orl> 



Ma 



Fig. 17.— Skull of Notidanus, side view (after Wiedersheim). 



pq. pterygo-quadrate cartilage (upper jaw) ; md. mandibular cartilage; nk. nasal 

 capsule; orb. orbit; r. rostrum ; ics. vertebral column, ►[« postorbital articula- 

 tion of the upper jaw with the cranium. 



Of the extinct family of Hybodontidce, a large series of specimens 

 is exhibited, the finest from the Lower Lias of Lyme Regis and the 

 Wealden of Fevensey Bay. The external form and the fins of 

 these fishes are not yet known, but it is very likely that they had 

 somewhat the proportions of the living Cestracion (Fig. 9). There 

 are two dorsal fins, each armed in front with a strong spine (Fig. 

 18). The skin is often covered in part with a dense shagreen ; and 

 on each side of the head there is a pair of large barbed hooklets, 

 fixed upon bony bases, which were originally regarded as teeth and 

 named Sphcnonchus by Agassiz. The skull is of a primitive type, 

 much resembling that of Notidanus ; and the teeth in some species 

 are also very similar to the early forms of the last named genus. 

 The precise limits of the generic type known as Hybodus have not 

 yet been satisfactorily determined ; but cuspidate crushing teeth 

 much like those of the Lias are occasionally met with in the Coal- 

 measures, and the latest species hitherto assigned to this form is 

 the little Hybodus dubrisiensis of the Chalk. Fine examples of the 

 nearly complete dentition are shown from the Lias of Lyme Kegis, 

 and also in the Wealden skulls from Pevensey Hay. The latter 



