VARIOUS SPECIES OF CTENODUS. 61 



1. Ctenodus ckistatus, Agassiz. 



Poissons Fossiles, Vol. III., p. 137, PI. XIX., fig. 16. 



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

 to ovate, 2i inches long, 1| inches 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 margin, and, being inclined to- 

 wards the anterior and posterior margins, assume a tendency to 

 a radial disposition ; the grooves between the ridges are angu- 

 lated ; 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 exhibiting 

 a coarse irregular granulation. 



The above description is of a palatal tooth which has the en- 

 tire right ramus of apparently the maxillary bone 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 con- 

 siderably 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 

 our specimens are scarcely so broad as that represented in the 

 "Poissons Fossiles," and they have likewise the posterior mar- 

 gin a little more produced. All the specimens are from the band 

 or dark shale overlying the Low-Main Coal Seam at Newsham. 



2. Ctenodus tuberculatus, n. sp. 



Tooth plate-like, thick, with an irregular ovate outline, 2f in- 

 ches long. If inches broad, the narrow end posterior ; the in- 

 ner margin gibbous or angulated in the centre ; the outer margin 



