VEETEBEATES. 377 



resources are iuadequate to a satisfactory conclusion, and the attempt to 

 limit them within definite specific bounds has resulted in the conviction 

 that it were more advisable, at this time, to notice not only the seemingly 

 distinctive characters by which each form may be recognized, but also to 

 carefully note those features of gradation which may seem to indicate 

 a probable specific identity. The same observations are equally appli- 

 cable to certain forms found in the subjacent division, or St. Louis lime- 

 stone, and which are consecutively noticed in the preceding pages. 



The above described form is represented by only a single perfect 

 specimen, that upon which the description is mainly based. This tooth 

 is most intimately allied to the laterally elongated teeth of the type of 

 Tanaoclus dbscwrus of Leidy, differing in a marked degree from the 

 typical examples of Antliodus, which latter may be defined as a Peta- 

 lodus having a very horizontal basal area and short root. It also bears 

 intimate resemblance to the St. Louis form mentioned under the name 

 T. pumilus, from which it chiefly differs in its relatively narrower 

 coronal folds and more shallow root. In specimens which have under- 

 gone much attrition, the basal bauds are more or less obscurely pre- 

 served — that along the convex crown-face is often quite obsolete, while 

 that which limits the opposite basal margin forms a more or less promi- 

 nent ridge, the imbrications of which may be entirely obliterated. 

 Also, individuals in the latter state of preservation have the concave 

 coronal region deeply excavated, while the inferior region presents 

 evidence of greater or less wear, and the root assumes a wedge-shaped 

 condition, strongly contrasting with its angular outline in perfect teeth; 

 indeed, but for the fortunate possession of specimens showing inter- 

 mediate stages of abrasion, the relationship of the extremely worn 

 examples of this form might be entirely overlooked. Moreover, the 

 latter bear evidence of wear in the roughened appearance of the coronal 

 surfaces, and the greater the extent of the abrasion, the more appa- 

 rent are its effects noticeable in the region along the basal angle of the 

 convex face, which is reduced in hight by the wearing away of the 

 coronal folds, in which process a more or less distinct sulcation is pro- 

 duced in the basal area just beneath the coronal angle, and after 

 extending the entire length of the tooth, and which may have been 

 caused by the wearing action along the line of impingement of the 

 contiguous tooth. The latter character, together with the attenuation 

 of the root, is sometimes observed in connection with teeth in which the 

 concave coronal region remains nearly perfect, and which forcibly recall 

 very similar features observed in the worn teeth of T.polymorplvus; but in 

 the latter case this is most probably a resemblance the result of similar 

 causes, since the differences (as the coronal ornamentation) which dis- 

 tinguish the perfect teeth of these forms one from the other are well- 



