NATURAL HISTORY OF CREATION. 



59 



rounded, covered with strong bony plates, and termi- 

 nating in a long tail, which seems to have been the sole 

 organ of motion. While the tail establishes this creature 

 among the vertebrata and the fishes, its teeth, chiselled, 

 as it were, out of the solid bone of the jaw, like the 

 nippers of a lobster, and its mouth opening vertically, 

 contrary to the usual mode of the vertebrata, enforce our 

 placing it near the crustaceans. The 'ptericlithys has also 

 strong bony plates over its body, arranged much like 

 those of a tortoise, and has a long tail ; but its most 

 remarkable feature, and that which has suggested its 

 name, is a pair of long and narrow wing-like appendages 

 attached to the shoulders, which the creature is supposed 

 to have erected for its defence when attacked by an 

 enemy. 



The lioloptychius is of a flat oval form, furnished with 

 fins, and ending in a long tail ; the whole body covered 

 with strong plates which overlap each other, and the 

 head forming only a slight rounded projection from the 

 general figure. The specimens in the lower beds are 

 not above the size of a flounder ; but in the higher strata, 

 to judge by the size of the scales or plates wdiich have 

 been found, the creature attained a comparatively mon- 

 strous size. 



The j)lacoids are now represented by the shark, stur- 

 geon, etc., of modern seas; the ganoids are all but un- 

 represented in our time. Of both classes, one invariable 

 peculiarity has attracted much attention. "In all 

 recent fish, with the exception of the shark family, the 

 sturgeon, and the long pike, the vertebral column ter- 

 minates at the point where the caudal fin is given off, 

 and this fin is expanded above and below the body, 

 forming what is called a homocercal tail. In all those, 

 without exception, which have been found in strata of 



