1883. 145 Trans. N. V. Ac. Set. 



submitted to the Academy, and will probably sufifice for the identifica- 

 tion of any similar fossils which may hereafter be found. 



Mylostoma. nov. gen. 



Ctenodipterme ganoids of large size, of which as yet only the denti- 

 tion is known. The teeth consist of strong and massive tables of 

 bony tissue becoming more dense and resembhng enamel above, 

 and forming pairs in the upper and lower jaw. The dental plates of 

 the lower jaw consist of long-oval or spatulate crowns, three to six 

 inches in length by one to two inches in width, and half an inch or 

 more in thickness, supported by strong, vertical, spatulate bones, 

 which project downward and backward, terminating posteriorly in 

 thin rounded margins. The upper surface of the crown of the in- 

 ferior dental plates is raised into a more or less prominent tubercle or 

 boss, which rises from the exterior margin a little anterior to the mid- 

 dle. The dental plates of the upper jaw are tables of dense tissue, 

 apparently forming two or more pairs on each side of the median line. 

 The largest of these is three inches in length, by an inch and a 

 quarter wide in the widest part, somewhat triangular in outline, flat- 

 tened where it rested on the probably cartilaginous floor of the crani- 

 um. It is about half an inch in thickness, the free surface somewhat 

 irregularly excavated to receive the prominences of the opposing den- 

 tal plates. Another of these palatal teeth is shorter and broader, with 

 one margin concave, apparently for co-adaptation with the tooth pre- 

 viously described. 



It is probable that we have not yet obtained all the elements in the 

 peculiar dentition of this fish ; and the parts yet discovered are so pe- 

 culiar and anomalous as to make it difficult to co-ordinate them satis- 

 factorily with any hitherto known. The flattened tabular dental 

 plates, which I have supposed formed the roof of the mouth, have a 

 general analogy in form and texture with those of ChimcBra, and, it is 

 evident, are their analogues and functionally their representatives. 

 Still the teeth of the under jaw, found with these and exhibiting the 

 same microscopic structure, differ widely from any portion of the 

 dentition of chimasroid fishes and exhibit a striking resemblance to the 

 dental plates of the Dipterine ganoids. They evidently form pairs ; for 

 we have the corresponding teeth of the right and left sides, and the 

 triturating surface oval in outline, though wanting the radiating ridges 

 of the Ctenodonts, seems to have occupied a corresponding position ; 

 and they are mounted on heavy vertical supports which, except that 

 they are flattened vertically instead of horizontally, correspond with 

 the splenial bones which support the dental plates of Ctenodus, 



The resemblance of the teeth, which I have supposed formed the 



