500 FISHES. 



system cannot be exactly determined ; thus Sphyrcenodus and 

 Eypsodon from the chalk of Lewes, and the London clay of 

 Sheppey. The American-' Por^Aews is allied to Hypsodon. 

 Another remarkable gemis from the chalk, Saurocephalus, 

 has been also referred to this family.^ 



Second Family — ATHBEiNiDiE. 



Body more or less elongate, sub-cylindrical, covered with 

 scales of moderate size ; lateral line indistinct. Cleft of the 

 mouth of moderate width, with the dentition feeble. Eye lateral, 

 large or of moderate size. Gill-openings wide. Vertebra} very 

 numerous. 



Small carnivorous fishes inhabiting the seas of the tem- 

 perate and tropical zones ; many enter fresh water, and some 

 have been entirely acclimatised in it. This family seems to 

 have been represented in the Monte Bolca formation by 

 Mesogaster. 



Atheeina. — Teeth very small; scales cycloid. The first 

 dorsal is short and entirely separated from the second. Snout 

 obtuse, with the cleft of the mouth straight, oblique, extending 

 to or beyond the anterior margin of the eye. 



The Atherines are littoral fishes, living in large shoals, 

 which habit has been retained by the species acclimatised in 

 fresh water. They rarely exceed a length of six inches, but 

 are nevertheless esteemed as food. From their general 

 resemblance to the real Smelt they are often thus misnamed, 

 but may always be readily recognised by their small first 

 spinous dorsal fin. The young, for some time after they are 

 hatched, cling together in dense masses, and in numbers 

 almost incredible. The inhabitants of the Mediterranean 



^ The systematic affinities of tliese extinct genera are very obscure. Cope 

 places them, with others (for instance Protosphyrmna, which has a sword-like 

 prolongation of the' ethmoid), in a distinct family, Saurodontidoe : see ' Ver- 

 tebrata of the Cretaceous Formations of the West," 1875. 



