8 



FOSSIL FISHES. 



FOSSIL FISHES.— GALLERY A. 



As the varied layers of sandstone, Jimestone, and clay, which com- 

 pose the greater part of the superficial crust of the earth, have 

 been accumulated as sedimentary deposits in lakes, estuaries, and 

 seas, one would naturally expect that, of the Vertebrate division of 

 animals, the remains of Fishes would be most frequently met with 

 in these formations ; and such is in fact the case, although from 

 their fragmentary condition, it is not always possible to determine 

 their precise systematic position. 



Fig. 1. — The " Lancelot," Branchiostoma lanceolatum (recent), a, Mouth ; c, vent ; 



b, abdominal pore. 



Some fishes have no hard structures which could be preserved iu 

 a fossil state. Thus, for instance, the simplest or most lowly 

 organized of fishes at the present day, the " Lancelet " {Branchios- 

 toma), has only a membrano-cartilaginous skeleton without vertebrse, 

 ribs, or jaws. (Fig. 1.) If in past geological times fishes of similar 



Fig. 2. 



Fig. 3. 



Fig. 2.— Tho "Hag-fish," Myxine australis (recent). 2a, Lower aspect of head. 2b, A 

 Single detached tooth of Myxine. 

 Fig. 3.— Mouth of Lamprey, Pctromyzon fluviatilin, showing circular arrangement of teeth. 



structure existed, they would leave no remains which could have 

 been preserved to us. 



