DEVONIC FISHES OF THE NEW YORK FORMATIONS 1 25 



the mandible is developed into a powerful cutting beak, usually much 

 facetted by wear. The marks of contact with the opposing pair of vomerine 

 elements were attentively examined by Newberry, who concluded that they 

 closed together in the following manner: "The incisorlike teeth of the pre- 

 maxillaries interlock with and shut over the projecting points of the turned 

 up mandibles, which are received into their concavities." Again, in describ- 

 ing these elements in D. t e r r el 1 i, he observes: "The inner [= poste- 

 rior] side is concave and frequently much worn and excavated by the promi- 

 nent extremity of the mandible, over which it shuts." ' 



Some distance behind the symphysial beak, the functional margin of 

 the lower dental plate rises again into a prominent projection, shorter, how- 

 ever, and less massive than the first, and appearing on the inner aspect as 

 a distinct riblike swelling, nearly vertical, and evidently in the nature of a 

 rudimentary tooth. From this point backward along the functional margin, 

 the lower dental plate is compressed into a thin edge, beveled somewhat on 

 the outer face by contact against the opposing element of the upper jaw. 

 In the majority of species, the margins of both upper and lower dental 

 plates are smooth and bladelike ; but a few, including the type, have them 

 denticulated as in Coccosteus. Vestigial remnants of a primitive Cerato- 

 dontlike denticulation occur in the lower dental plates along the abrupt 

 downward slope of their posterior margin ; that is to say, in a position cor- 

 responding to that in which they are seen in the upper. 



The line of fusion between the lower dental plate, in the strict sense of 

 the term, and the supporting ossification, which we take to be the splenial, 

 is marked externally by a prominent constriction, starting from a point 

 slightly behind the functional margin, and extending in a curved line down- 

 ward and forward until reaching the bottom point of the anterior or sym- 

 physial margin. Seen from the external aspect, the lower dental plate thus 

 appears to be set ofT from the slender, elongate shaft of bone which we iden- 

 tify as splenial, by means of a conspicuous shoulder, underneath which 

 there runs a groove for the lodgment of portions of the Meckelian cartilage. 



' Newberry, J. S. Ohio Geol. Sur. Rep't. Pal. 1875. v. 2, pt 2, p. 5, 29. 



