309 



Superior maxillary. 



Lines. 



Extreme length of bone 58 



Length of bone internally 43 



Breadth posteriorly 23 



Diameter fore and aft of large postero -internal dental area 18 



Diameter of same transversely 12 



Diameter fore and aft of anterior dental area 11 



Diameter of same posteriorly and transversely 5 



Diameter fore and aft of external dental area 16 



Diameter transversely of the same where widest 5 



EUMYLODUS. 



EUMYLODUS LAQUEATTIS. 



Among some fossils from the Cretaceous sandstone near Columbus, Missis- 

 sippi, submitted to my examination by Dr. William Spillman, there is a spec- 

 imen of the maxillo-dentary apparatus of a chimseroid fish, related with 

 Ischyodus, but apparently distinct from that genus. The specimen is repre- 

 sented in Figs. 21, 22, Plate XIX, and Figs. 13, 14, Plate XXXVII. It 

 most resembles, in its general form, the mandible of Ischyodus, as repre- 

 sented in Fig. 20, Tab. 40, of I. Townsendi, and Fig. 16, Tab. 40 c, of /. 

 Agassizi, of the third volume of the Atlas of the Poissons Fossiles. 



The bone is of denser character than the corresponding one of Edaphodon, 

 and in this respect and several others is more like that of Leptomylus, de- 

 scribed by Professor Cope. 



The outer surface (Fig. 14, Plate XXXVII) is nearly flat, but slightly 

 depressed below, and bent outwardly behind from the triturating surface. 

 The inner surface (Fig. 21, Plate XIX) is fluted ; the anterior third presents 

 a succession of three curved ridges separated by two grooves ; the median 

 third forms a wide, concave groove ; and the posterior third forms a nearly 

 square plane, sloping from the triturating surface backward and inward, and 

 defined by a subacute border from the outer surface of the bone. 



The anterior border of the mandible appears as curved cylindroid termina- 

 tion of the bone. No appearance of a distinct symphysial surface exists. 



The oral surface (Fig. 22, Plate XIX) is uneven, and conforms in its out- 

 line with the inner and outer faces of the bone. The anterior most promi- 

 nent portion is convex, and exhibits some scratches and polish, due to its 

 masticating function. Its posterior two-thirds incline from a median dentary 

 ridge, moderately without and behind, but steeply within. 



