PISH OF THE CARBONIFEROUS PERIOD. 19 



this species distinguish it easily from its congeners; the steep, 

 striated margin is also peculiar. The puncturing of the surface 

 rather coarser than that of the H. turgidus (Ag.). I have seen 

 several specimens from the Armagh limestone. 

 {CoL Cambridge University.) 



Chomatodus ohliquus (M^Coy). 



Sp. Char. Obliquely rhomboidal, transversely elongate ; apex 

 marginal, obtusely pointed; middle of the tooth obliquely 

 tumid or convex; attenuated sides flattened or slightly con- 

 cave ; ends obtusely pointed or rounded ; surface highly po- 

 lished and perfectly smooth except at the apex, vv^hich is coarsely 

 punctured ; basal margin surrounded by a broad imbricating 

 fold of ganoine*, increasing to three or four on the ends of 

 some of the teeth. 



This species differs from the C. cinctus (Ag.) in its obliquely 

 rhomboidal flattened form and marginal apex, as M^ell as having 

 but one fold of ganoine at the middle of the basal margin. In 

 some examples the ends are equal and the v^^idth three times the 

 length, in others the ends are unequal, and the length two-thirds 

 of the width, but in all the apex is marginal and the general 

 form obliquely rhomboidal, the basal margin having a down- 

 ward curve nearly opposite the apical projection of the anterior 

 margin, and between the two extends the oblique mesial con- 

 vexity. Length averaging 4 lines. 



Rare, in the carboniferous limestone of Armagh. 



{Col, Cambridge University and Capt. Jones, R.N. &c.) 



Chomatodus denticulatus (M^Coy). 



Sp. Char. Transversely oval, base about three times wider than 

 long; middle elevated into a compressed, obtusely pointed 

 cone, about equal in height to the short diameter (length) of 

 base, from which a sharp, much compressed mesial ridge ex- 

 tends on each side to either end, its cutting edge being broken 

 into numerous obtuse, compressed denticles decreasing in size 

 towards the ends ; the notches which separate the little cones on 

 the edge give rise to obtuse sulci, defining them a short way 

 down the sides ; surface smooth ; base surrounded with three 



* 1 provisionally use this term (trom yavos, splendour) to designate that 

 peculiar, dense, modification of dentine wiiich forms the highly polished 

 surface of most fish-teeth, and which is not unfrequently confounded with 

 the true enamel of the teeth of the higher animals ; the latter is however 

 secreted by a distinct organ quite external to and independent of the den- 

 tine, while the false enamel which I propose to call ganoine is merely pro- 

 duced by the calcigerous tubes of the dentine becoming suddenly straighter, 

 closer and more numerous as they approach the surface. 



b2 



