VERTEBRATES. 97 



Deltodus angularis, N. and W. 



PI. IX, Fig. 1. 



Posterior teeth of small size, triangular in outline, thiejk; 

 crown surface marked with a sharp, narrow, oblique keel, 

 which runs from the prominent posterior summit. This is 

 bordered by a broad and deep sub-central furrow, from which 

 the surface runs into a broad, flattened ridge, which borders 

 the straight side; entire enamel surface finely punctate. 

 Antero-posterior diameter, 1 inch. 



Figure 1 represents a posterior tooth seen from above, natural size. 

 Formation and locality : Coal Measures, La Salle, Illinois. 



Deltodus stellatus, N. and W. 



PI. IX, Figs. 2, 3, 3 a. 



Posterior tooth spirally revolute, obliquely triangular in 

 outline, both angles of the broader extremity somewhat round- 

 ed, a sharp, prominent keel runs from the larger basal angle 

 to the pointed summit. From this ridge the surface descends 

 abruptly to the nearest margin, more gradually into a well 

 defined sulcus, which runs along the opposite border ; enameled 

 coating is marked with a few faint lines of growth, parallel 

 with the broader margin, and obscure longitudinal grooves or 

 wrinkles, is uniformly porous throughout, the pores being rela- 

 tively large, angular in outline, many of them stellate ; length 

 1 inch, 9 lines ; breadth 1 inch, 1 line. 



The posterior teeth of this species will be readily recognized by their narrow 

 triangular form, remote transverse lines of growth, the angular keel, the longi- 

 tudinal plication, and particularly by their coarse, angular, sometimes stellate 

 porosity. 



The anterior teeth are strongly revolute, transversely arched, the base round- 

 ed and expanded into a ring-like angle on one side, where there is a broad, 

 shallow, marginal furrow or depression. The surface markings are similar to 



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