152 NEW ZEALAND NATURE-STUDY BOOK 
cup-shaped depression. The centrnm of one vertebra is 
joined to that of the next along the rims of these cups, so 
-that a hollow space is left between the two. This is filled 
with an oily fluid, which helps the edges to move freely 
upon each other. From the upper and lower surfaces of 
the centra in the caudal vertebrae two spines project for 
some distance—i.e. one from each surface, the length of 
these varying considerably. Hach spine curves backwards, 
and forms at its base a conspicuous arch. 
The mouth of the fish is well provided with teeth, 
which are usually small, numerous, and sharp, and are set in 
the jaws in such a way as to point backwards towards the 
throat. There are no grinding or tearing teeth. The 
structure and position of the teeth often throw a good deal 
of light on the habits of the animal to which they belong. 
For example, the absence in the fish of grinding and tearing 
teeth teaches us that the prey is swallowed whole. The 
backward slope and sharp points of the teeth enable the 
fish to seize and hold the struggling slippery animals on 
which they feed. Some fish have teeth specially shaped for 
crushing the shells of molluscs—the Schnapper is able to use 
its powerful jaws and teeth for this purpose. 
THE FLOUNDER. 
General Description. The body of the Flounder is 
boat-shaped, with the broadest part slightly nearer the 
head than the tail. The purpose served by this arrange- 
ment has already been explained. The upper side is dark 
and convex, whilst the under side is almost white and 
relatively flat, the whole being covered with closely fitting 
scales, which are easily.removed. On both sides the 
lateral line is well marked, the red colour on the under 
side rendering it very conspicuous. The head is small and 
flat and carries on its upper surface a pair of eyes placed 
