196 PALEONTOLOGY OF ILLINOIS. 



bed stratum near the base of the Carboniferous series at Santa Fe, 

 New Mexico. The state of preservation of the specimens, although 

 not perfect, is sufficient to afford the basis of comparison with the 

 allied species Orthopleurodus carbonarius, occurring in the Coal 

 Measures of the Mississippi Valley. While the present species is 

 smaller in size, the mandibular posterior teeth differ from the latter 

 in their proportionately greater breadth as compared with the length 

 along the antero-lateral border; the maxillary posterior teeth may 

 be distinguished by the apparently less oblique course of the coro- 

 nal ridge, while the surface punctation is much the same in both 

 species, the punctse, perhaps, more widely spaced in the New Mex- 

 ican teeth. Its resemblances with the above species is more inti- 

 mate than with Orthopleurodus convexus, although there is a marked 

 similarity in the maxillary posterior forms, as indicated by the 

 imperfectly worn examples. 



Geological position and locality: From the fish-bed layer near the 

 base of the Carboniferous series, associated with other Lower Car- 

 boniferous fish-remains; near Santa Fe, New Mexico. 



