on fossil fisn-teeth. 307 



Ceratodus Oblongus. n. s. 

 PI. XV.— Figs. 7, 8. 



Tlie only specimen we have of this variety is unfortunately imperfect. 

 But there would seem to be abundant ' groimd for separating it from 

 .all the others already noticed ; both from its general form and re- 

 lative proportions. It is of the flatter five ridged group of teeth. It is 

 broader than any of the others, and is evidently an old, and much worn 

 tooth. The inner edge is peculiarly straight for two thirds of its length, 

 when it suddenly bends outwards at an angle of about 130". There is a 

 very obtuse, and slightly marked ridge or elevation along the inner 

 edge, and between this and the ridges of the spurs of the tooth, there is 

 a depression. The first horn is blunt, but slightly projecting, and is 

 marked by a continuation of the low ridge or elevation which bounds the 

 tooth on the inner edge. The second horn or spur is sharp, very pro- 

 minent, and rises by nearly one^half its depth, above the general surface 

 of the tooth. The continuation of it forms a ridge which is nearly 

 parallel to the outer edge of the anterior spur ; and which does not, as 

 in the other species, converge to, or nearly to, the centre of the inner 

 edge of the tooth. The third horn, or spur, has apparently been very 

 prominent, but in the old specimen before us it is obliquely worn down 

 to an irregular surface, which has removed the elevated projection, of 

 the top or point of the spur. The continuation of its ridge also is nearly 

 in a line parallel with the anterior inner edge of the first horn. The 

 furrows between these horns are comparatively broad, rounded, and de- 

 pressed. 



The posterior portion of the tooth is unfortunately broken off. 



The bony layer is strong, massive, and thick, with, as in all the others, 

 a furrow or continuous curved depression along its entire length. 



The surface is beautifully punctulated and has besides little, nearly, 

 circular, depressions or fossettes, irregularly disposed. In addition the 

 ■whole surface is beautifully striped in irregular contour lines, giving 



