BUFFALO SOCIETY OF NATURAL SCIENCES 179 



bed, at Eighteen Mile Creek, for they demonstrate that this typically 

 Onondagan species ranged into the Genesee. This is not surprising, 

 since remains of Onychodus have been recorded from the Chemung. 

 The surprising thing is — if all these remains really belong to a single 

 species — that Onychodus sigmoides should be represented both in 

 fresh (Chemung) and in salt water (Conodont and Onondaga lime- 

 stone). 



The mandible of Onychodus described below is of unusual interest, 

 since it affords for the first time a knowledge of the structure of this 

 element in the genus. The specimen (PI. 58, fig. 3 and text-fig. 59) 

 consists of about two- thirds of a left mandible; it lacks the anterior, 

 or symphyseal end, as well as the posterior extremity. The upper 

 margin is set with slender, sharply-pointed laniary teeth placed at wide 

 intervals, and not all of the same size. Some of them had apparently 



Fig. 59. Onychodus sigmoides Newberry. Restored Outline of Mandible 

 Shown in Plate 58, Figure 3 



All the elements composing it are shown — the dentary above, angular below, and 

 the articular, at the extreme right, wedged in between these two. The front end of 

 the mandible is restored after a specimen from the Delaware limestone of Ohio. 

 Onondaga Limestone; Leroy, N. Y. E 2556. 



become worn through use, or else had been broken off before preser- 

 vation. The mandible clearly indicates the presence of several dis- 

 tinct elements; first, a dentary element {den.), a narrow element in 

 which the teeth are set, extending the entire length of the preserved 

 portion of the mandible. Second, an angular (ang.), situated below 

 the dentary, and extending forward about two-thirds the length of the 

 mandible. Third, an articular element (art.); the bone itself is 

 absent in the specimen, but its position is clearly indicated by the 

 sutural lines and facets on the angular and dentary. It was wedged 

 in anteriorly between these two elements. 



It has been customary in describing the mandibles of the Crosso- 

 pterygii, to refer to all the elements below the dentary, as infraden- 

 iaries, except the most posterior one, which has generally been called 



