304 ON FOSSIL FISH-TEETH. 



apex of the tooth ; and thence it gradually drops to the level of tlw 

 anterior horn. 



The first horn, or projecting point is obtuse, and on its upper surface 

 becomes, after use, worn down to a slightly concave or depressed furrovr, 

 which passes up towards the apex of the tooth. The second horn is 

 sharper, and more prominent, and the line of its continuation is marked 

 by a blunt ridge, which continues in a slightly curved line towards 

 the apex, until at about half the distance it loses itself in the general 

 concavity of the surface of the tooth. The third spur is similar, but the 

 ridcfe which marks its continuation on the upper surface of the tooth 

 is more marked and continuous. This ridge, in worn teeth, is separated 

 from the last or terminal ridge, (which terminal ridge is at the extreme 

 edo-e) by a deep furrow forming a sharp depression between the third 

 and fourth, or last, horn. PI. xv. Tigs. 1 and 2. 



The internal edge of the teeth is formed of a nearly vertical surface 

 of bright enamel, marked by numerous crossing strise of growth, and 

 forming a regular wall of enamel of nearly an inch in height — (y^yths). 

 This enamelled surface is continued all round the tooth. (PI. xvi. Fig. 4. 

 PI. XV, Figs. 1 — 4.) Where worn above, the surface is, as usual, closely 

 punctulated, but is also marked by numerous little depressions, which 

 are often confluent, and are transverse to the length of the tooth, thus 

 causing a series of small transverse, irregular, and ill-marked furrows on 

 the surface. 



As compared with the great thickness and size of the enamel layer, 

 the bony layer of the tooth is thin and small, not being much more than 

 one-fourth the thickness of the former. It is marked below by a deep 

 furrow, or concavity, passing along the greater portion of the length of 

 the tooth, and by a thickening of the mass, forming a rudely projecting 

 process, just beneath, or in a line with the apex of the tooth. 



The lower-jaw tooth ofthis species is shewn in PI. xv. Figs 3, 5, 6. As 

 .in the preceding species, its outline forms a marked contrast with that 



