Pisces. | UPPER PALAZOZOIC VERTEBRATA. 623 
most specimens crenulated. Average length of the posterior tooth is about one inch four lines, and its width 
one inch, 
This species varies considerably in the outline of the different specimens, and I think it is very doubtful 
whether it is truly of the genus, on account of the flatness and slight inrollment of the teeth, and the 
little definition of the characteristic oblique ridges; the strong crenulation of the margin is also a character 
which I do not recollect to have seen in Cochliodus, but recalls the observation of Capt. Jones, (in Portk. 
Geol. Rep.) that the Cochliodus magnus, he thinks, pass into the Helodus planus, which may be borne out 
by a large suite of specimens, although I have not yet myself seen the passage. 
Position and Locality—Common in the lower carboniferous limestone of Armagh ; in the lower limestone 
of Lowick, Northumberland; and in the carboniferous limestone of Kendal. 
CocHLIoDUS OBLONGUS (4g.) PI. 3. H. fig. 19. and Pl. 3.1. fig. 28. 
Ref.—Portk. Geol. Rep. t. 14a, fig. 5. 
Dese.—P osterior tooth elongate, narrow, subeylindrical, oblong, obliquely subtruncate, elliptically pointed at 
about an angle of 45° behind; anterior margin nearly at right angles to the long axis of the tooth; anterior 
ridge very small, almost obsolete, scarcely defined from the equally wide flattened space between it and the 
second oblique ridge, which is strongly defined on each side, but narrow and only moderately convex ; posterior 
ridge very large, exceeding twice the width of the middle ridge, separated from the middle one by a broad, 
moderately concave suleus, rather more prominent than the middle ridge, broadly and moderately convex, 
abruptly rounded at its anterior edge, but gradually sloping towards the posterior end; surface as in the C. 
acutus. Length of rather small specimens about one inch two lines, of middle ridge only two lines. Middle 
and anterior teeth unknown. 
This species is very easily distinguished from all the others by the great size of the posterior ridge, which is 
frequently twice and half as wide as the middle one, and rarely only double, while in the C. acutus and contortus 
it forms a mere narrow, raised margin. The form of this species is also narrower and more cylindrical. Although 
a common species I have not yet seen the anterior or middle teeth. It was in a specimen of this species collected 
by the Rev. W. Stokes, M.A. of Caius College, that I first saw the vertical mode of succession of the teeth, the 
young one being distinctly visible beneath the level of the old one from a transverse fracture ; one end of the 
specimen magnified half a diameter is represented on our Plate 3. I. fig. 28, and shews on the upper surface of 
the old tooth the anterior and middle ridges, and the oblique sulcus, which separates the latter from the poste- 
rior ridge, which is broken across by the section ; the fractured edge shews the inrollment of the outer margin 
of the tooth, and the whole thickness of its substance, shewing the vertically tubular structure of the superficial 
half, and the two denser layers which form its concave under or dorsal surface. At about the thickness of the 
substance of the old tooth lower down is seen the young tooth, exactly concentric to it in outline, and having its 
structure similarly displayed in the section; and on its upper surface is seen not only the same punctured surface, 
but the same oblique ridge as in the old one (this requires a magnifying glass to be seen distinctly in the figure). 
I might here caution the observer that the inrollment displayed by the old tooth is the extreme extent to which 
it occurs ; so that it would be impossible (as was suggested to be by an excellent authority) that the supposed 
young tooth could be a continuation of a large inrollment, which is also rendered impossible by the appearance 
of the oblique sulcus noted on the little tooth. The other half of the same specimen I have had polished, and 
it is represented on our Plate 3. H. fig. 19. 
Position and Locality.—Common in the lower carboniferous limestone of Armagh. 
Explanation of Figures.—P|. 3. H. fig. 19, transverse polished section magnified, two diameters of speci- 
men shewing the succession of the teeth. PI. 3. I. fig. 28, posterior tooth, rough fracture, shewing the vertical 
succession of the teeth, with young tooth in sitw magnified one and half diameters. 
[rasc, 11. | 4L 
