from the Shales of the Northumberland Coal-field. 83 
1. Ctenodus cristatus, Agassiz, 
Poissons Fossiles, vol. iii. p. 137, pl. 19. fig. 16. 
Tooth plate-like, rather thin, irregularly elliptical, inclining to 
ovate, 24 inches long, 13 inch broad; the upper surface 
somewhat hollowed or concave; the inner margin well 
arched, the outer much less so; the whole surface is covered 
with twelve close-set, transverse ridges, which are studded 
from end to end with closely arranged conical tubercles ; 
the ridges increase in size as they approach the outer mar- 
gin, and, being inclined towards the anterior and posterior 
margins, assume a tendency to a radial disposition; the 
grooves between the ridges are angulated ; the tubercles are 
perfect only at the outer margin, where they are covered 
with a coat of brilliant chatiel and here they are seen to 
- have the outer face flattened, the base of each tubercle or 
denticle being subtriangular ; elsewhere they are much worn 
and somewhat compressed at the sides in the direction of the 
ridges, the whole surface of the tubercles and ridges exhi- 
biting a coarse irregular granulation. 
The above description is of a palatal tooth which has 
the entire right ramus of apparently the maxillary attached. 
The tooth itself is considerably more than half the length of 
the bone, the posterior extremity of which is very wide and 
truncate. 
Four or five other specimens have occurred; but they are 
considerably worn, the tubercles in some instances having 
almost disappeared; two are mandibular, two palatal; the 
former are very much narrower than the latter. 
There can be little doubt that this is Agassiz’s species, 
though my specimens are scarcely so broad as that represented 
in the ‘ Poissons Fossiles,’ and they have likewise the poste- 
rior margin a little more produced. All the specimens are 
from the band of dark shale overlying the Low-main coal- 
seam at Newsham. 
2. Ctenodus tuberculatus, n. sp. 
Tooth plate-like, thick, with an irregular ovate outline, 2? inches 
long, 1§ inch broad, the narrow end posterior; the inner 
margin gibbous or angulated in the centre; the outer mar- 
gin a little convex; the surface is slightly convex, and is 
furnished with twelve or thirteen deep, sharp, parallel, ap- 
proximate ridges, which. are strongly tuberculated towards 
the outer margin, and divided by narrow, deep, angulated 
grooves ; they are arched posteriorly and enlarged towards 
the exterior border, but do not at all assume a radial ar- 
