624 



HISTORICAL GEOLOGY. 



Modern Isopods are seldom over two inches long. The basal joint of a leg 

 of the Prasarcturus was three inches long, and three quarters of an inch 



980-983. 

 980. 



980 c 



980 a. 



982. 



PlAcoderms.— Fig. 980, Cephalaspis LyelU (x|); 980 o, same, with pectoral fins in place; 980 6, c, scales; 

 981, Coccosteus decipiens, side view; 981 o, dorsal plates; 982, Ptericlithys MiUeri (xi) ; 983, Pterichthys 

 cornutus. Figs. 980, 981, Agassiz ; 981 o, 983, Traquair ; 982, Pander. 



