6 PALJaONTOLOGY OF OHIO. 



thys, but it may be said here, in passing, that it is on the same general 

 plan with that of Dinichthys, and, in some respects, is strikingly similar 

 to that of D. Hertzeri. 



Comparing Dinichthys and Lepidmiren, a surprising similarity is at 

 once apparent, and it may be said that the dentition of Dinichthys Ter- 

 relli is almost exactly like that of Lepidosiren annectens, except that it is 

 more than a hundred times larger. 



This similarity is well shown in the subjoined wood-cuts, which repre- 

 sent the dentition of both, one of the size of nature, and the other about 

 one-tenth the natural size, linear. 



Dentitios op Lefidobiben annectens, Owen. 



Front and side views of head, natural size, drawn from specimen. 



From these figures it will be'seen that the dentition of Lepidosiren con- 

 sists of mandibles which have almost the exact form of those of Dinich- 

 thys TerrelU, and have the same structure and functions. In Lepidosiren 

 the anterior extremity of each mandible rises into a prominent tooth, 

 while, behind this, the upper margin presents, first, a ridge or fold, which 

 produces a subordinate denticle, and then, for about one-third the length 

 of the mandible, is a sharp edge of enamel. At its posterior end this is 

 slightly denticulated, as though with rudimentary teeth, as in Dinichthys. 

 In the upper jaw we find two dfental plates, more or less perfectly joined 

 at the symphysis, and forming, first, by a strong anterior fold on either 

 side, prominences which are functional teeth, and which match the pro- 

 duced extremities of the mandibles. Behind these, on each side, is a 

 second ridge or fold, and then a wing-like plate of enameled bone, which 

 plays upon the corresponding edge of the mandible. The most cursory 

 examination of the figures and descriptions of the dentition of Dinich- 

 thys will show that it corresponds closely to this pattern. 



In Lepidosiren there are also two small, pointed teeth (" nasal, " Owen • 

 " vomerine," Huxley) which overhang and precede the dentition that has 

 been described. JSTo teeth corresponding to these have been discovered 

 with the remains of Dinichthys, but this is not strange, for even if the 



