YEBTEBRATES. 3!)1 



ity of typical specimens of D. princeps, measuring in greatest Light 

 1 inch, lateral diameter of crown .77, elevation of concave face .57, 

 elevation of convex face .45, lateral diameter of base .50, depth beneath 

 base of concave crown-face .40 inch. We strongly suspect the form here 

 indicated -will be found to represent a part of the somewhat varied 

 dentition of the above referred to species. 



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

 IiUnois. 



Dacttlodtjs minimus, St. J. and W. 



PI. XIII, Fig. 19. 



Teeth minute, of robust proportions. Crown lozenge-shape as seen 

 from above, rather depressed or tumid, crest gently arched laterally, 

 strongly so from the concave face, obtusely rounded; convex face ellip- 

 tical in outline, lateral extremities sharply rounded, gently arched in 

 both directions, basal margin gently arched downward in a less degree 

 than the crest, slightly eccentric at one or other extremity, and bordered 

 by a faintly denned, narrow coronal fold ; concave face broadly oval in 

 outline, strongly arched and obtusely acuminate along the crest line, 

 but slightly depressed vertically and gently arched laterally, giving the 

 surface a full though not tumid appearance, basal margin gently and 

 quite regularly arched downward and outward, moderately prominent 

 and produced beyond the basal region to which it is abruptly inbeveled, 

 coronal folds very obscure or obsolete. Base massive, thick, in width 

 scarcely more than half the lateral diameter of the crown, obliquely 

 produced in the direction of the concave face, in depth equalling if not 

 exceeding the elevation of the crown, and divided into three or four 

 radicles, well-defined from the narrow basal area, which forms. an acute 

 angle with the convex crown-face. Greatest diameter of crown .08 

 inch, anteroposterior diameter .06, elevation of convex face .04, great- 

 est depth of base .10 inch. 



The description is founded upon a unique and well preserved specimen 

 belonging to the collection of Mr. Van Horne. In diminutiveness 

 this little tooth almost rivals some of Polyrhizodi which we have 

 described. The coronal portion bears a somewhat marked resemblance 

 to some of the narrow, obtusely crested Chomatodi ; but the very strong, 

 lobed base seems to indicate generic identity with Dactylodits — its 

 abbreviated lateral dimensions and depth of base offering well-marked 

 distinctions from Polyrhizodus. In the present state of our knowledge, 

 it is impossible to detect other than congeneric affinities with the other 

 forms of Bactylodus known from the same horizon. 



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

 Illinois. 



