502 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britaun. 
size very much, and range from the large size of the specimen figured down to- 
about an inch in diameter, the latter, no doubt, being the teeth of younger fishes. 
Nothing definite is known as to the arrangement of the teeth in the mouth. 
Hitherto no specimens have been found which exhibited the relationship or relative. 
position of the teeth to each other. It is probable, however, judging from the 
worn surface of the central: portion of the tooth, that those of the lower and upper 
jaws formed a corresponding cutting and triturating surface the one to the other, 
but whether they existed in a simple double row extending backwards along the 
palate and corresponding to the two rami of each jaw, as might be inferred from 
the sinuosity of the coronal surface of P. sznuosus, Davis. (vide page 504), or 
they were arranged in concentric rows as in some of the large sharks at present 
existing, there is no evidence to prove. In either case the strong, deepiy- 
implanted, many-barbed root indicates considerable power as well as voracity, 
especially if compared with the somewhat weak and meagre attachment of the 
teeth in modern sharks. 
Locality : Comparatively abundant in the Carboniferous Limestone of Armagh. 
Ex, coll. Earl of Enniskillen. 
Polyrhizodus colei, Davis. 
(Pl. LX., figs. 9, 10.) 
Teeth, breadth across the crown 2 inches, height from tip of root to summit of 
the crown 1°5 inch. Anterior surface of the crown large, convex, oval in form 
with depressed lateral prolongations, extending considerably beyond the extension 
of the root. The centre of the crown is ‘9 of an inch from the anterior ridge to its 
summit. It is much worn, the portion of the surface most constantly used being 
distinctly indicated by its appearance. ‘The inclination of the surface of the crown 
to the posterior ridge is about 60°. The surface is smooth and beautifully polished, 
it possesses almost a transparent appearance, and the ramification of the nutrient, 
vessels is well defined. The lateral portions of the surface which are not worn to 
any great extent do not exhibit this peculiarity, but are covered with minute punc- 
tures. ‘The anterior ridge is doubly curved, upwards from each lateral extremity 
and downwards to the middle portion of the crown ; it is smooth and partakes of 
the general characters of the crown. The posterior surface of the crown is deeper 
than the anterior: it 1s concave and bounded on its lower margin by a high ridge 
which appears to have consisted of a single fold produced from the body of the 
tooth. The root at its base is 1°5 inch across; towards its extremity it spreads 
out to 16 inch. It is divided into six (or occasionally seven) large club-shaped 
rounded rootlets, which retreat from the posterior, and bend forward towards the 
anterior face of the tooth. The radicles are separated by an interspace one-half 
their own diameter between each. 
