SAURICHTHYS. I7l 



Spams, and many other fishes. The central linear pulp-cavity 

 extends, as also in the conical teeth of many fishes, to the extreme 

 apex of the dentine : the cells of the ossified pulp were occupied by 

 an opaque substance in the tooth examined : at its periphery and 

 through the whole of the base of the tooth were scattered numerous 

 coarse cells. The true dentine presented a mahogany brown colour : 

 the main calcigerous tubes of this substance radiate through it at 

 right angles to the periphery of the tooth, and with a sHght curvature, 

 the concavity of which is turned towards the apex of the tooth. The 

 tubes give off many small lateral branches, which are curved, with 

 their concavity directed towards the pulp-cavity, or to the base of the 

 stem : they diminish in size as they approach the external enamel- 

 like substance, pass across the well-defined boundary which sepa- 

 rates this substance from the dentine, and then are immediately 

 resolved into fasciculi of the extremely fine and slightly diverging 

 fibres or minute tubes which form the only appreciable structure in 

 this enamel-like substance. These fine lines have a general direction 

 at right angles to the periphery of the tooth, like that of the calcige- 

 rous tubes of the dentine, from which they are continued ; but many 

 of them are bent in different directions, so as to cross each other, in 

 the manner described and figured in the corresponding clear external 

 enamel-like substance of the tooth of the Lepidotus ; they are, 

 however, somewhat larger and diverge in straighter lines ; they finally 

 terminate in fine calcigerous cells at the periphery of the tooth. 



The thickness and structure of the dense external enamel-like 

 layer, the length and form of the pulp-cavity, and the texture of the 

 ossified remains of the pulp with which it was filled, are decisive 

 against the reptiUan character of the Saurichthys. Its affinities to 

 that class are manifested only in the outward form of the tooth, and 

 the dense, minutely-tubed tissue of the dentine, a structure, however, 

 which is common to the teeth of all the Sauroid fishes. 



DENDRODUS. 



66. Dendrodus biporcatus. — The teethindicative of the genus, for which I 

 have proposed the name of Dendrodus {I ) , occur sparingly and detached in 



(1) SivSpov a tree, "£'«? a tooth ; in reference to its internal dendritic structure. 



