On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 505 
curve along the anterior median ridge, and straight crest of the coronal region 
appear, however, to be sufficiently indicative that they all belong to the same species, 
and that the difference in size represents only periods of orowth, 
A difference in form may be noted in this species which could not be easily 
observed in a symmetrical one. The peculiar curve in the median ridge in some of 
the teeth proceeds in the contrary direction to the one described above, and in place 
of the more attenuated extremity of the coronal surface being towards the right of 
the tooth, it is towards the left side. his difference leads to the inference that the 
_ teeth were in pairs in the mouth. 
Locality: Mountain Limestone of Armagh. 
Ex coll. Earl of Enniskillen. 
Polyrhizodus attenuatus, Davis. 
(IE, JLnx,, sme, i144.) 
Teeth, extremely elongated in proportion to their height; length 1°8 of an 
inch ; height 5 of an inch. Crown elliptical, narrow, sli ghtly convex, compressed 
to a thin, acutely-pointed, slightly-serrated edge along the nearly-straight crest ; 
laterally the coronal surface is depressed towards the acutely-pointed lateral angles. 
The anterior margin forms a prominent ridge at a right angle to the basal area, 
almost straight in the median region, slightly rounded towards the base at each 
end ; a single enamelled fold extends along its entire length; posterior fuce of the 
crown considerably deeper than anterior, shie@htly concave in each direction ; shoht 
striations extend from the minutely denticulated crest down the surface ; lateral 
extremities obtusely rounded, with a slightly-raised border ; basal border broad, 
with seven or eight delicately imbricating folds, moderately elevated above the 
coronal surface—more so above the basal area, from which it is separated by a 
groove. The anterior basal area occupies a space about equal to that of the crown. 
It is concave, and gently rounded towards the roots ; upper surface distinctly pus- 
tulate, the spots placed indiscriminately, without arrangement ; near the base of 
the rootlets, a peculiar series of duct-like striations terminating in a prominent 
pustule attached to each at its upper termination. |Downwards the strize 
descend to, and are absorbed in the general mass of the roots. The root 
divided into a variabie number of radicles. The largest number is, perhaps, on the 
specimen figured, there being twenty-two. The radicles circular in section are 
irregular in size, and vary on the same specimen from ‘2 to ‘1 of an inch in length, 
the shorter ones generally being thin and small. The coronal surfaces are enve- 
loped in a coating of ganoine, preserved on their lateral expansions, but generally 
worn off in the centre by the attrition of the grinding and cutting surfaces of the 
teeth. Where the surface beneath the enamel is exposed by its removal it is seen, 
when magnified, to be full of nutrient ducts, which ramify along the surface, with 
many devious sinuosities, 
4H 2 
