Animal Dentition 293 
the Tench and the Carp, which subsist very largely upon water- 
plants, having the most powerful pharyngeal teeth. In the 
carp these teeth (Hig. 15) are arranged in two or three rows, 
the innermost row including a single tooth, the second having 
in some cases two rather larger ones, while those of the third 
row are the largest and most complex of all. In these the 
front one is the largest and has a smooth crown; the crowns 
of the others, when unworn, beimg sculptured. 
The last type of fish dentition to which I have space to 
allude is adapted to a purely carnivorous diet, and is presented 
by those voracious fishes known as Barracuda-Pikes (Sphyrena), 
which are relatives of the mackerel and the thunny. In one 
of the largest species the lower jaw (Fig. 16) is armed with a 
formidable array of sharp, lancet-hke teeth, arranged in a single 
series, there beg about twenty-four of these in each side of the 
jaw, and their size gradually increasing from back to front. In * ©: Dae aoe 
the upper jaw they are opposed by a double series of similar teeth, 
into the interspace of which they fit when the mouth is closed. In addition, there are 
also nine or ten lancet-shaped teeth on the palate which present the peculiarity, rare 
among fishes, of being implanted in separate sockets. As a rule the alternating teeth 
are shed, so that the formidable dentary apparatus is always maintained in a thoroughly 
efficient condition. Teeth of extinct barracuda-pikes are met with in the Tertiary 
deposits of Hurope; but the antecedent Cretaceous seas must have absolutely swarmed 
with huge fishes armed with teeth more or less closely resembling those of the 
barracudas, and frequently inserted in distinct sockets. When the so-called coprolites 
of the Cambridge Greensand were worked for artificial manure, no vertebrate remains 
Were more common in the phosphate heaps than the spear-like teeth of the fish 
then known as Saurocephalus lanciformis, but now called Protosphyrena feror. An 
American Cretaceous fish of this type, 
known as Portheus molossus, must have 
been an even more formidable monster, 
attaining probably a length of twelve 
or fifteen feet, and thus perhaps dis- 
puting the tyranny of the ocean with 
the great swimming lizards which 
abounded at the same epoch. 
Unlike what was the case in earlier periods of the earth’s history, when the 
fishes were either predaceous sharks and rays, or were for the most part encased in 
complete suits of impenetrable armour of quadrangular enamel-coated plates, the seas 
of the Cretaceous epoch swarmed with thin-scaled fishes much like those of the 
present day, which must have fallen an easy prey to the barracuda-like Portheus 
and Protosphyrena. Among the most common of these Chalk fishes were species 
closely allied to and in some cases generically identical with the existing Hoplopteryx 
and Beryz, commonly known as Slime-Heads. 
Fig. 16. Lower Dentition of a Barracuda-Pike. 
