VERTEBRATES. 41 



Antliodus similis, N. and W. 



PI. II, Figs. 10, 10a. 



Teeth rather small, thick and strong; crown twice as broad 

 as high, upper margin regularly arched, obtuse or sub-acute; 

 anterior surface semi-elliptical, not quite half the height of the 

 tooth, arched both vertically and laterally, smooth and polished 

 except where worn ; upper margin striated, lower slightly bow- 

 shaped; posterior surface rather more than twice the height of 

 the anterior, curved in both directions ; lower margin marked 

 with fine, imbricating folds, and forming a thin, prominent 

 edge; root short, thick. 



This species approaches very nearly, in form, to A. robustus, but is smaller, 

 and the angle formed at the edge of the crown, by the anterior and posterior 

 surfaces, is larger, giving to the tooth, as it stands vertically, a somewhat flatter 

 top. This difference is most clearly seen in the profile sections of the two 

 species. The root also projects more anteriorly. So like, however, are the two 

 species, that if they had been found at the same geological horizon, they would 

 with propriety have been considered mere variations in form, of one and the 

 same species. * 



Figs. 10 and 10a represent the anterior face and profile section of the nat- 

 ural size. 



Formation and locality : Keokuk limestone, Warsaw, Illinois. 



Antlioihjs cucullus, N. and W. 



PI. Ill, Figs. 1, la, IS. 



Teeth of rather large size, robust, elliptical in outline, much 

 broader than high, superior border regularly arched, thickened, 

 rounded, striated and obtuse ; posterior face of crown sub-ellip- 

 tical, smooth, terminated below by a broad, flattened coronal 

 ridge, which is arched downward and marked indistinctly with 

 imbricating folds; anterior face of crown lenticular in outline, 

 half the height of posterior face, regularly arched laterally, 

 terminating in long, acute points, slightly concave vertically, 

 —6 



