430 On the Fossil Fishes of the Carboniferous Linestone Series of Great Britain. 
surface. Anterior margin curved sigmoidally, conforming to the shape of the 
crown, comparatively thin and acuminate, lateral margins straight, forming a 
slight ridge projecting beyond the edge of the base. 
Posteriorly the surface of the crown is convoluted, folding over with a helix- 
like coil, the lateral margins of which converge until they form an obtusely 
pointed angle. The base is thick and strong, especially where the ridge of the 
crown is highest, becoming thinner anteriorly ; in structure it is coarser and 
openly striated. 
Connected with the posterior tooth a second one (see PI. LII., fig. 9), hitherto 
regarded as a separate species under the name Pecilodus parallelus, has been 
found, which leaves no room to doubt that it is in its natural position, and 
from the character of its inside margin leads to the natural inference that a 
third tooth occupied the frontor median portion of the lower jaw. The second 
tooth is triangular and “narrow, very much inrolled spiraliy, the curve exceed- 
ing a semicircle.” Length 6 mch ; anterior breadth ~4 inch, converging back- 
wards to a recurved point. A median ridge, occupying the major portion of the 
surface of the crown, extends from the anterior margin backwards to the pointed 
apex ; a second ridge is also present forming the lateral margin of the crown, and 
between this and the median one there is a depression extending between, 
and parallel with, the two ridges. The surface is more deeply sulcated than 
that of the first tooth, but this is probably accounted for by the tooth being 
subjected to a smaller amount of attrition. 
Included in the collection are examples of teeth which approach near to an 
equilateral triangle; they are proportionately much broader across the anterior 
margin and shorter laterally than the second pair described above ; posteriorly 
they form an acute point slightly recurved, in other respects they are the 
counterpart of the second tooth and it is probable that they were connected 
with it, and formed the median tooth on each side the symphysis of the lower 
jaw. 
The more or less pointed posterior apex of the teeth composing this species, and 
their ever widening anterior margin, together with the parallel sulci and ridges 
which extend transversely across the surface have very much the appearance 
that would be presented if they marked lines of additional growth and there 
can be little doubt that these teeth have increased in size by successive additions 
to their anterior margin. The general form and character of the teeth are ab- 
normal and have no living representatives at the present time, so that it is 
extremely difficult either to reconstruct the general form of the mouth or to 
obtain a correct idea of the zoological position of the fish. Judging, however, 
from the paucity of its remains, there can be little doubt that it was a cartil. 
aginous one, and from its association with fishes of elasmobranch structure, and 
animals of marine growth and habits, it may possibly be inferred with safety 
