74 CATALOG OF POSSIL PISHES IN THE MUSEUM 



of a ridge rising obliquely upward and forward; this does not, how- 

 ever, rise above the cutting edge so as to form a secondary cusp, as 

 in Dinichthys. Symphyseal denticles present (not well-shown in the 

 type). 



Remarks. — Besides the type we have three other specimens of this 

 species, from the type locality. In general shape, and in the demar- 

 cation of the functional from the inserted portion, these elements are 

 not unlike a Dinichthys mandible. But the long, slender form, and 

 the absence of a secondary cusp back of the beak, clearly mark them 

 as belonging to the genus Stenognathus as defined by Newberry. 



From Stenognathus gouldi, the Ohio species, the present form is dis- 

 guished, first, by the much weaker beak; second, by the presence of 

 symphyseal denticles, whereas in the Ohio species their place is 

 occupied by a rounded vertical ridge, which extends, like the row of 

 denticles, about two-thirds down the height of the blade. In the pres- 

 ent species, also, the functional portion is not quite so slender as in 

 the Ohio form; i.e., the mandible of this species is closer to Dinichthys 

 than is that of S. gouldi. 



The other three mandibles of this species (paratypes), are from the 

 type formation and locahty: 



E 1933 An imperfect left mandible, lacking the beak and the pos- 

 terior half of the inserted portipn. It shows well the 

 region of junction between the functional and blade por- 

 tions, and the excavation along the lower margin of the 

 functional portion for the attaching tissues. This region 

 resembles that in Dinichthys. The cutting edge agrees 

 with that of the type specimen in the absence of a sec- 

 ondary cusp. 



E 1938 Anterior portion of a mandible. The specimen is somewhat 

 deeper than the type and probably represents an older 

 individual. It shows the S5miphyseal region weU; this 

 is turned inward at right angles to the outer face and 

 terminates in a vertical row of denticles, extending about 

 two-thirds down the symphyseal margin. The denticles 

 themselves are missing, but the roots of two of them are 

 clearly shown; the lowermost one is the largest. 



E 2506 Inserted portion of a mandible. 



