VERTEBRATES. 373 



and T. bellieinctiis. The wedge-shaped condition of root is more or less 

 prevalent in all these forms — in T. prcenuntius and T. depressus as a 

 permanent feature apparently, while in the other named forms it is 

 evidently, in part at least, the result of accidental causes. These 

 peculiarities are strongly suggestive of generic importance, but in view 

 of the uncertainty (which may indeed exist only in the mind) of their 

 permanence, it is deemed more consistent with the nature of the facts 

 possessed to retain them provisionally in the same generic association. 

 Indeed were it possible to study the complete dention of the forms enu- 

 merated, even a more intimate specific relationship might be proved 

 than can be derived from the study of the isolated material now acces- 

 sible. 



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

 Illinois; Pella, Iowa; St. Louis, Missouri. 



Tanaodtjs sctjlpttjs, St. J. and W. 



PI. XI, Kg. 20, 21, 22, 23. 



Teeth small, presenting as viewed from above a somewhat variable 

 oval or broad elliptical outline. Concave crown-face broad elliptical or 

 irregularly circular in outline, but subject to considerable variation in 

 this respect — in some examples more or less hexagonal, in others trian- 

 gular or curvilinear — lateral extremities acutely or obtusely rounded, in 

 some of the more circular teeth less distinctly defined, nearly plane or 

 more or less depressed in the middle, and rising into a low, regularly or 

 eccentrically arched, obtuse crest, which slightly projects beyond the 

 basal line of the opposite face, the lower margin is generally less regu- 

 larly and more angularly arched downward, more or less produced and 

 in some examples sharply inbeveled to the base, and bordered by five 

 to six well-defined, narrow imbricating folds, which pass round the lat- 

 eral angles in a broad abruptly curved belt, which merges into the nar- 

 rower though equally well-marked basal baud of the convex face ; the 

 convex crown-face presents a low, lenticular outline, nearly jdane verti- 

 cally and broadly arched laterally, the crest and inferior margin nearly 

 the same in curvature, the basal margin being gently arched downward 

 in the middle, sometimes angularly so, and again gently curved towards 

 the extremities, forming an obtuse angle with the basal area from which 

 it is well-defined by the imbricated coronal band, except in examples 

 which have suffered from attrition, in which the folds as well as the 

 peculiar sculpturing in the entire surface are obsolete. The lower por- 

 tion of the concave face' is elegantly sculptured, presenting a delicate 

 tracery of undulating and frequently interrupted lines, variously dis- 

 posed ,'Jbut~most frequently slightly deflected to one or other side, or in 



