192 PALAEONTOLOGY OF ILLINOIS. 



so far as the meagre materials at the present time in hands per- 

 mit of being determined. 



The earliest representatives of the genus occurring in American 

 rocks were discovered by Mr. Springer in Lower Carboniferous 

 strata, probably of Chester age, of New Mexico; the typical repre 

 sentative species, Orthopleurodus carbonarius, belongs to the Upper 

 Carboniferous, the upper division of which has afforded the majority 

 of specimens thus far, although apparently the same species is not 

 unfrequently met with in deposits near the base of the Coal 

 Measures. 



ORTHOPLEURODUS CARBONARIUS, (N. and W. sp.) pars. 



PL XIII, Fig. 6, 8. 



Sandalodus carbonarius, NEWBERRY and WORTHEN, 1866, 111. Geol. Surv., II, p. 104, pi. X 

 f . 4, 5. 



Deltodus angularis, NEWBERRY and WORTHEN, 1866, 111. Geol. Surv.. II, p. 97, PI. IX, f. 1 



A singularly interesting group of teeth discovered by Mr. L. A. 

 Fuller in the shales over Coal No. 5 of the Illinois General Section 

 of Coal Measure strata, at Bloomington, leaves little room for doubt 

 respecting the specific identity of the above cited forms, and with 

 which is associated a third form probably holding a position imme- 

 diately in advance of the posterior tooth of the mandibles, that 

 originally described under the name Deltodus angularis. This 

 "second" or median tooth of the mandible is distinguished by its 

 triangular outline, straight postero-lateral border corresponding in 

 coadaptation with the articular border of the above mentioned pos- 

 terior tooth, and the uniform depressed coronal contour. A similar 

 tooth has been obtained from the Upper Coal-Measure strata near 

 Topeka, Kansas, where individuals of the long posterior teeth of the 

 upper jaw (Sandalodus carbonarius) have also been found ; and only 

 recently Professor Worthen has brought from the Upper Coal strata 

 at LaSalle, representatives of all three forms. The generic diagno- 

 sis, founded on the typical specific forms belonging to the present 

 species, sufficiently describes the individual characteristics of the 

 various dental elements here ascribed to it. 



The group of teeth discovered by Mr. Fuller, which bear every 

 appearnce of having belonged to one and the same individual, pre- 

 sent the following proportionate measurements : Maxillary posterior 

 tooth, greatest preserved length along the straight border 18 mm. ; 

 greatest breadth 7 mm. ; breadth at broken extremity 6 mm. Pos- 

 terior tooth of mandible, greatest length from posterior extremity to 



