OF CREATION. 2 75 



Placoids (chiefly rays and sharks), while no less than 

 forty-four are distinctly referable to existing families 

 of the Ctenoid and Cycloid orders ; most of the latter 

 are very nearly allied to existing species. 



Among the principal families of fish represented 

 in the London clay of Sheppey are those of which 

 the perch, the mackarel, the blenny, the herring, and 

 the cod are the respective types. The species of 

 the perch family are by far the most numerous of 

 the Ctenoid fishes (those having the scales jagged 

 like the tooth of a comb), while those allied to the 

 mackarel are equally predominant among the Cy- 

 cloids. It appears, that, of about a hundred and 

 forty -four Cycloid and Ctenoid species of fishes which 

 now inhabit the seas surrounding the British Islands, 

 there are seven species of the perch, eleven of the 

 mackarel, twenty of the cod, eight of the herring, 

 and eight of the eel families ; and referring to the 

 whole number (about forty-four) of the fossil species 

 of the two first-mentioned orders found in the Lon- 

 don clay of Sheppey, we meet with the same num- 

 ber of species (seven) of the perch tribe, twelve 

 species of the mackarel, four species of the cod, two 

 of the herring, and one of the eel family, while four 

 others of the most abundant recent families are 

 either totally absent or very sparingly represented. 

 On the other hand, there is, besides these, one family 

 now almost confined to the southern seas, but repre- 

 sented in the London clay by three distinct genera ; 

 another (now absolutely tropical), by a genus nearly 

 related to the existing tropical form ; while a third, 

 which includes the common sword-fish, a species of 

 which, inhabiting the Mediterranean, sometimes 



