VERTEBRATES. 101 



little inequality of surface, but are marked by bands of color. 

 The triturating surface is evenly granulo-punctate, except along 

 the margins of the narrower end, which are- vermicularly 

 roughened. 



This species is distinguished from the others, now or heretofore described, 

 by its more oblong or rhomboidal outline, the lateral margins not converging to 

 a common point ; the more oblique one forming another angle before reaching 

 the pointed extremity. The ridges of the surface are also parallel, whereas in 

 most other species they converge. Length, 1 inch, 10 lines; breadth at base, 

 1 inch. 



Figure 8, represents the superior surface seen from above, natural size. 



Formation and locality: St. Louis Limestone, St. Louis, Missouri. 



Deltodus grandis, N. Sp. 



PI. IX, Pig. 9, 9 a. 



Teeth of large size, thick and strong, triangular in outline, 

 spirally convoluted. An obtuse, angular ridge runs from the 

 obtuse angle of the broader extremity to the narrower end, 

 from which the surface falls off laterally into a deep sulcus, 

 which converges toward the same point; the acute angle of the 

 broader end is strongly elevated. The enameled surface is 

 highly polished and smooth, except where showing a few faint 

 lines of growth parallel with the broader margin. It is uni- 

 formly punctate throughout, and where most worn the orifices 

 of the enamel tubes form simple pits in a smooth surface ; 

 where it has suffered less abrasion it is minutely shagreened by 

 elevated rings about their orifices. 



The specimen before us affords an interesting illustration of the severity of 

 the duty performed by these teeth when in use, a piece having been broken 

 out of its most prominent part during the life of its possessor; the edges of 

 the fracture being rounded by subsequent wear, its bottom and sides being 

 coated with a new deposit of enamel. 



Figures 9 and 9 a, represent the upper surface and profile, natural size. 



Formation and locality : Keokuk limestone, Warsaw, Illinois. 



