VERTEBRATES. 369 



referred to under the above genus with which it is here associated. The 

 tooth is very small and delicate, and so imbedded as to reveal only the 

 basal and convex coronal aspect. Viewed from below, the basal area 

 presents an irregular trapezoidal outline, a little broader at one extremity 

 than the other and rounded or obliquely truncated, gently arched out- 

 ward along the concave border, beneath which is situated the low, com- 

 paratively short root. The basal margin of the convex face is slightly 

 arched inward, and defined by a simple coronal fold, which forms the 

 well-marked angulation between the basal area and the convex crown- 

 face, which latter is low, nearly plane, gently arched along the crest, 

 which is produced beyond the basal line, and gradually declines in eleva- 

 tion from the broader extremity, and interrupted by delicate vertical 

 sulci which produce a faint denticulate appearance. Lateral diameter 

 of crown about .23 inch, antero posterior diameter .10. 



The sublimate outline shorter, relatively wide, and more strongly 

 arched concave border, also the more central position of the root, con- 

 stitute the more prominent features which distinguish the present form 

 from its congenus. In its short lateral extent it bears resemblance to 

 Antliodus; but the straight convex margin and vertical inequality in 

 the crest line present characters more or less strongly in contrast with 

 the symmetrical outlines of the typical examples of the latter group. 



Position and locality: Upper beds of the St. Louis limestone; Alton, 

 Illinois. 



Tanodus pumilus, St. J. and W. 



PI. XI, Fig. 1,2,3,4,5. 



Teeth small, moderately strong though variable in proportions, crown 

 moderately compressed or rapidly thickening towards the base, broadly 

 arched along the crest, sometimes obscurely denticulated near the 

 extremities, and usually projecting at a considerable angle beyond the 

 basal margin of the convex crown-face; the concave face is irregularly 

 elliptical in outline,in some examples the longer sides converge towards 

 one or other extremity giving rise to a more or less subtriaugular outline, 

 very gently arched laterally and slightly depressed vertically, basal mar- 

 gin slightly undulating in its downward and outward course, and defined 

 by a very wide basal band composed of five or six imbricated folds, from 

 the upper margin of which the plain coronal surface ascends at a slight 

 angle, lateral extremities inequally and more or less acutely and 

 obliquely rounded or truncated; the convex face is about half the hight 

 of the opposite side, irregularly lunate in outline, gently arched laterally 

 or sometimes strongly so in laterally abbreviated, acuminate examples, 

 nearly plane vertically, basal margin generally very gently arched 



