PRESIDENT'S ADDRESS. Ixv. 



Pycnodontidae : Lepidoius, Pleuropholis, Pholidophorus, Ophiopsis, 

 Histionotus, Aspidorhynchus, and Belonostomus occur in this 

 county. 



At the commencement of the Cretaceous Age a great change 

 took place in the fish-Fauna. The most remarkable was the 

 depletion of the Ganoid, and the predominance of the Teleostei, 

 a few isolated types, however, lingered during the Lower 

 Cretaceous Age, when their extinction became nearly complete. 

 The London Clay of the Island of Sheppey has yielded about 

 100 species of fish-remains, of which 19 are Rays and 10 Sharks. 

 Among the Ganoids Pycnodus and Gyrodus have left their teeth. 

 All the other forms belong to Teleostei. Among the 

 40 genera only 4 are now living and are restricted to the 

 tropical seas ; the rest are extinct. The Lower Eocene Beds of 

 the Paris basin, in addition to scales of the Ganoid Lepidosteus 

 (now found living, only in North America), yield a large 

 number of shark's-teeth. The Calcaire of Monte Bolca, near 

 Verona, contains an important deposit of fish-remains. 



Preraspidse, Cephalaspidse, and Placodermi are distinguished 

 from all other Ganoids by the development of the exo-skeleton, 

 recalling to mind such osseous fishes as the Mesozoic Siluridae, 

 which are separated by a considerable gap in point of time. 

 At all events it is reasonable to consider the Selachii, and more 

 certainly the Placodermi, to be derived from the ' primitive 

 Ganoidei. The relations between the Ganoidei and the Teleostei 

 are so close that is is difficult to decide the point of departure, 

 but taking everything into consideration the Siluridae {Cat-fish} 

 may prove to be that point. Towards the close of the Tertiary 

 Age, Fishes show a relationship with those now living. There 

 is a marked difference between the Fish of the Upper and 

 Lower Tertiaries. In the latter their living representatives are 

 restricted to the tropics, in the former, especially in the Pliocene, 

 to the temperate regions. Those of the Pliocenes of Sub- 

 Appenine Italy, the Roussillon of Southern France, Malta, and 

 Egypt, the Crags of Belgium and England almost without an 

 exception belong to genera now living in the adjoining seas. 



