76 



HARDWICKE'S SCIENCE-GOSSIP. 



microscope, and also in the hope of obtaining by this 

 means some clue to its family or genus. The sec- 

 tion showed very evidently that the tooth was a new 

 one, that it belonged to the class of fishes, andj^if 

 one could judge from such small data as a single 





\> 



^>^ 





Fig. 60. Vertical Section of largest denticle, x 80. 



tooth, that it was a Selachian; for no long tissue is 

 attached to its base, and it was clearly not inserted 

 in a socket. The tooth is very small, being only 4^ 

 in. in height and t;\ in. in breadth : its shape is 

 that of a shortened cone, the point being slightly 



Fig. 61. Vertical Section of Tooth of Ciewop/ycAiMS, x 20. 



rounded, giving the tooth a rather squat appear- 

 ance. Microscopical examination shows that it is 

 composed of unvascular dentine, M'ith a layer of 

 enamel all round the free edge. The pulp-cavity 



proceeds '-gV ill- up the tooth. At its commence- 

 ment it is very broad, stretching from enamel to 

 enamel ; but as it passes up the tooth it rapidly 

 contracts, so that when it has proceeded ,'gth of an 

 inch, the cavity is only ^V in. broad : from this point 

 it gradually becomes narrower. The dentine varies 

 in its thickness according to the shape of the pulp- 

 cavity. The tubules which ramify in it are very 

 numerous and exceedingly fine, varying from 

 in. to -^rnhrn in. in diameter ; they do not 



the 



20000 •"■ '" 30000 



branch or anastomose except when close to 

 periphery, some of the branches being so fine that 

 I cannot measure them. The tubules spring from 

 the pulp-cavity and proceed in straight lines ; their 



Fig. 62. Vertical Section of two denticles of Ctenoptychius, 



X 80. 



course is parallel with the axis of the tooth, and 

 those that arise from the sides of the cavity have 

 a slight tendency outwards. The enamel borders 

 the whole of the free edge of the tooth ; at the 

 base it is unsupported by the dentine, and forms 

 one of the boundaries of the pulp-cavity; its 

 average thickness is 1-1777 in. : no structure can be 

 detected, although I have examined it under a 

 power of about COO diameters ; nor do any of the 

 dentinal tubules pass into it, as is generally the 

 case in fish-enamel. 



Until I am more certain that these are really 

 newly-discovered teeth, 1 shall not attempt to 

 name or classify them, for I do not wish to commit 



