• of Climaxodus and Janassa. 325 



occupies its correct position by the side of the upper central 

 tooth. A third Petalodontoid tooth lies a little apart, and pro- 

 bably belongs to tliis jaw. 



On another small slab recently obtained there is a fine speci- 

 men of a second lateral tooth associated with a secondary tooth. 



From the above it ajipears that there is evidence enough to 

 show that in Climaxodus^ as in Janassa^ the teeth are placed 

 in transverse rows of seven teeth each, one being symmetrical 

 and central, and six lateral, three on each side, the extreme 

 lateral tooth on either side being Petalodontoid in form, that 

 there are more rows than one, and that they are placed in both 

 upper and imder jaws. In fact it is quite evident, not only 

 that the teeth in Climaxodus agree in external character 

 with those in Janassa^ but that they also agree with them in 

 the mode of arrangement. 



The minute structm-e of the teeth in the two so-called ge- 

 nera is very similar. In both, the centre of the tooth is com- 

 posed of osteo-dentine, having branched anastomosing medul- 

 lary canals, Avhich are for the most part arranged lengthwise, 

 and give off from their sides rather coarse tubules into the 

 surrounding matter. The canals likewise send off compara- 

 tively small branches, which subdivide dichotomously as they 

 approach the periphery of the tooth. Here many of them 

 abut perpendicularly to the surface. The walls of these small 

 branches assume the character of dentine, and the interstices 

 between them are filled up with opaque white matter — proba- 

 bly cement ; so that, by the unequal wear of these peripheral 

 components, the surface of the tooth is always kept rough, 

 having the granular and punctate appearance before spoken 

 of. When quite fresh, there is a thin film of enamel cover- 

 ing the surface ; but this seems to disappear rapidly with 

 the use of the tooth. 



The teeth of both Climajcodxis and Janassa agree with the 

 above general description ; but in the latter the material ap- 

 pears more dense, and the cement is in greater abundance and 

 is distributed more regularly than it is in Climaxodus ; con- 

 sequently it is found to assume a pretty regular reticulated 

 appearance on the surface when a little worn down. 



The generic identity, then, of Climaxodus and Janassa 

 seems pretty certain ; and as tlie latter was established many 

 years (1882) before the f(n-mer (1848), the genus Climaxodus 

 must merge into that of Janassa. Ultimately, perhaps, Pcta- 

 lodus will be found to be more closely related than can at pre- 

 sent be demonstrated ; for it is not only in the Petalodontoid 

 form that a resemblance is observed, but likewise in the primary 

 teeth themselves, which show a remarkable similarity in ge- 

 neral form to some of the Pctalvdonfes. 



