208 



GEOLOGY. 



Fig. 118 



strong helmet with two circular holes in front for the 

 eyes. The chest and back were covered by a curiously- 

 constructed cuirass formed of plates, and the tail was 

 sheathed in a flexible mail of bony scales. The arms are 

 also covered with plates. There are peculiarities in the 

 jointing of the different parts of this bony covering, and 

 in the contrivances for securing lightness with strength, 

 which are very curious. Hugh Miller says of it that, 

 " with its inflexible cuirass and its flexible tail, and with 

 its two arms, that combined the broad blade of the pad- 

 dle with the sharp point of the spear, it might be regard- 

 ed, when in motion, as a little subaqueous boat mounted 

 on two oars and a scull." He farther says that " when, 

 in laying open the rock in which it lies, the under part is 

 presented, as usually happens, we are struck with its re- 

 semblance to a human figure, with the arms expanded, 

 as in the act of swimming, and the legs transformed, as 

 in the ordinary figures of the mermaid, into a tapering 

 tail." The correctness of this description can be seen in 

 Fig. 119. The Cephalaspis, or "buckler-head," 3, Fig. 

 118, is so called from the shield-like shape of the bony 

 head-plate, which is all in one piece. 



