VERTEBRATES. 77 



by transverse undulations conforming to the inner margin, the 

 narrow intervening grooves showing coarse and irregularly elongate 

 punctae which elsewhere present at the triturating surface merely 

 circular orifices spaced by twice or thrice their own diameter. The 

 original specimen measures in transverse diameter between the 

 inner angles about 38 m m. ; greatest length above 50 m m. 



The above species was originally described from a unique imper- 

 fect example, and the very few subsequent accessions are even 

 more fragmentary, and none are sufficiently entire to give the exact 

 proportions of the perfect tooth. The fragments are, however, 

 readily recognizable by their peculiar coronal contour and transverse 

 undulations. In the light of these imperfect data, there appears to 

 be specific identity between the Keokuk teeth and a couple of 

 fragments of the same forms discovered by Mr. Van Home in the 

 Warsaw beds ; the Keokuk specimens are more worn and present a 

 less strongly undulated surface than obtains in the Warsaw 

 examples, which otherwise, in outline, proportions and general 

 coronal contour, agree well with the Keokuk teeth. A fragment of 

 another specimen, from the St. Louis formation, near Pella, Iowa, 

 representing a tooth of the ordinary size attained by the present 

 species, is also undistinguishable from the individuals just mentioned. 

 The present form presents marked contrasts with that noticed from 

 the Chester formation under the head of Taniodus obliquus, as 

 remarked in the observations appended to the diagnosis of the 

 latter species. 



Geological positions and localities : Keokuk limestone, Warsaw and 

 Hamilton, Illinois. Also, sp. ?, Warsaw limestone, above Alton, 

 111. ; and sp. ?, St. Louis formation, Pella, Iowa. 



T^ENIODUS KEGULARIS, St. J. and. W. 



PI. XIII. Fig. 11. 



Teeth of large size. Maxillary posterior (?) form subhrhomoidal 

 in outline, moderately arched in the direction of inrollment. 

 Antero-lateral border very oblique in its forward and outward 

 course, the coronal belt nearly vertical and comprising half 

 the height of the border, a slight sulcus defining it from the basal 

 portion, the inferior edge of which is broken away; postero-lateral 

 border almost parallel with the opposite side, making an angle of 

 about 55 with a line drawn between the angles of the inner 



