FISHES. 



121 



country. Since that time they have been found in the 

 Silurian, Devonian, and Carboniferous formations of Britain 

 and North America, and they have been stated to occur in 

 later deposits {e.g., Upper Trias). As regards their size, the 



Fig. 493. — Outlines of some forms of " Conodonts," greatly enlarged, a, A simple form 

 {Acodiis acutits, Pander) ; b, Transverse section of the same ; c and d, Two compound forms, 

 from the Lower Silurian of Russia ; e. Another compound form from the Carboniferous of 

 North America. (After Pander and Newberry.) 



" Conodonts " are always very small, the most of them, per- 

 haps, between a thirtieth and a twentieth of an inch in 

 length ; though there are other bodies apparently of the 

 same nature which sometimes reach a tenth or even a 

 quarter of an inch in length. In their /o?'m they are ex- 

 tremely variable, though all the typical kinds have an ex- 

 ceedingly close resemblance to the teeth of different kinds 

 of Fishes. The simplest forms are slender cones, usually 

 more or less bent, hollow at the base, pointed at the end, 

 with sharp opposite margins (fig. 49-S, a). Others (fig. 493, 

 c) consist of a principal tooth, with a basal horizontal pro- 

 cess bearing a row of small teeth. Others, again, have a 

 central primary tooth, flanked by minor secondary cones on 

 each side (fig. 493, d), thus reminding one forcibly of the 

 teeth of Hylodus. Others (fig. 493, e) have an elongated 

 base carrying a row of small cones on one side, the central 



