300 ON FOSSIL FISH-TEETH. 



CeEATODUS HlSLOPIANUS. N. S. 



Plate xiv. Figs. 1—7. Plate xvi. Fig. 1. 



Of this marked variety we have three specimens helonging to the 

 same jaw of the elevated class, (or upper-jaw) and two of the more flat- 

 tened (or lower-jaw) opposite sides. 



The outline, in plan, of those which we suppose to have belonged to 

 the upper jaws of the fish, is rudely an isosceles triangle, the two shorter 

 sides of the triangle being slightly curved, the longer side being formed 

 by an imaginaiy line joining the terminations of the horns, or projecting 

 points of the external side of the tooth. The inner sides are of nearly 

 equal length, that which was postei'ior being slightly more curved and 

 shorter than the otlier. Of the ridges of the tooth, the first, or that which 

 on Agassiz's supposition was placed foremost in the mouth, is, as com- 

 pared with the others, flattened and broad, and in the old and worn teeth 

 becomes worn down into a slightly concave irregular furrow or depression 

 along the middle. Its point or termination is obtusely rounded. The 

 second horn is sharp, and forms a very marked projection separated by a 

 deep bay or furrow from the first. The line of its continuation is marked 

 on the surface of the tooth by a ridge, which passes in a riglit line to tlie 

 highest point or summit of the tooth. The third horn or ridge is similar to 

 the second, and is even more prominent, and strongly marked, and the 

 continuation of its line is equally marked by a sharp ridge passing also 

 in a right line to the apex of the tooth. The posterior horn was large, 

 strong, and well marked, being also much sharper, and less obtuse 

 than the first or anterior horn (PI. xiv. Fig. 2,). Seen in profile, the 

 outline of these upper-jaw teeth rises in a continuous slope from the 

 anterior part of the tooth to the central apex, and gradually falls from 

 that to the posterior point of the tooth also. fFig. 2. PI. xiv.) The 

 upper surface of the teeth, where they have been exposed to wear, ex- 

 hibits in perfection the curiously punctulated surface common to all 

 these teeth: but is also marked by small irregular and partially conflu- 



