from the Shales of the Northumberland Coal-Jield. 83 



1. Ctenodus crtstatus, Agassiz, 

 Poissons Fossiles, vol. iii. p. 137, pi. 19. fig. 16. 

 Tooth plate-like, rather thin, irregularly elliptical, inclining to 

 ovate, 2^ inches long, 1^ 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 enamel, 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 tuherculatus, 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 ; tlie 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- 



