588 



HISTORICAL GEOLOGY. 



its head-shield). The surface of the former is (as usual with the species) 

 covered with small tubercles (Fig. 885 a), while the latter has a minutely- 

 pitted surface. A restored iigure of a foreign species is shown on page 557. 



886. 



Placoderms. — Fig. 885, Cephalaspis Dawsoni (x |), Lankester; a, tubercles of surface; 886, C. Campbell- 



tonensis (x |), Whiteaves. 



The posterior, or caudal extremity, of the C. Daiosoni is so very short, 

 relatively to the breadth of head, that the fish must have been poor at 

 sculling — its chief means of locomotion. Any relation to the Trilobites 

 is set aside by the tubercular surface. Lankester states that it belongs to 

 the subdivision of the genus which he calls Encephalaspis. 



887-889. 



889. 



887. 



888. 



DiPNOANS. — Fig. 887, Coccosteus occidentalis (x|) ; 888, Macropetalichthys Sullivantl (x J-x^j) ; 889, Acanthaspis 



armata (x |). From Newberry. 



Among the Dipnoans of the period there was a species of Coccosteus^ 

 C. occidentalis of Newberry ; only the posterior dorsal plate (Fig. 887) is 

 known ; its surface is in part fine-tuberculate. Fig. 888 represents the 



