174 PALAEONTOLOGY. 



the dorsal and pectoral of some kinds, are soft or 

 jointed ; the malacopterans are abdominal or apodal, 

 have free operculated gills, and the swim-bladder has 

 an air-duct. 



The carp, pike, herring, salmon, eel, exemplify this order, 

 but the species of all these genera which have left their 

 remains in tertiary strata — and none of them are older — are 

 distinct from the existing kinds. 



The Ganoids in these formations are reduced to the genera 

 Lepidosteus and Acipenser ; but may have been represented 

 by the palates with crushing teeth, from the Sheppey clay, to 

 which the names Pisodus* and Phyllodus^ have been given. 



With respect to the fishes of the tertiary period, " they 

 are so nearly related," says Agassiz, " to existing forms, that 

 it is often difficult, considering the enormous number (above 

 8000) of living species, and the imperfect state of preservation 

 of the fossils, to determine exactly their specific relations. 

 In general I may say that I have not yet found a single 

 species which was perfectly identical with any marine exist- 

 ing fish, except the little Capelin (Mallotus villosus), which 

 is found in the nodules of clay of unknown geological age in 

 Greenland." These nodules are mostly very recent, and ex- 

 emplify the operation of the dissolving soft parts of the fish 

 in consolidating the surrounding matrix. 



No class of animals is more valuable in its application to 

 the great point mooted by UniformitariaDS and Progressionists 

 than that of fishes ; for their testimony is exempt from the 

 objection on the score of the defective nature of negative evi- 

 dence, to which the Progressionists' conclusions from the 

 known genetic history of air-breathing animals may be open. 

 It is true that many creatures living on land are never carried 

 out to sea ; but marine deposits may be expected to yield 



* See Owen's Odontography, p. 138, pi. 47, fig. 3. 

 f Ibid., p. 139, pi. 47, figs. 1 and 2. 



