VEETEBRATES. 71 



supposed opposed form of the upper jaw, the lateral borders more 

 gradually converge the anterior position and greater prominence of 

 the coronal ridge, while the inner margin is less obliquely rounded 

 than obtains in the corresponding forms of the last described species. 

 Geological position and locality: Upper fish-bed of the Kinderhook 

 formation; Burlington, Iowa. 



PSEPHODTJS? SYMMETRICUS, ST. J. and W. 



PL I, Fig. 6, 7. 



The present species is represented by a single form, with which 

 only one or two individuals, of doubtful generic relations, have thus 

 far been provisionally identified. The form corresponds to that re- 

 ferred to the median position on the lower jaw. The typical example 

 is that of a tooth below medium size, sub-trapezoidal in outline, 

 moderately arched from within outwards and somewhat closely in- 

 rolled, giving to the outline a relatively great breadth as compared 

 to the length of the tooth. The outer margin and coronal region is 

 worn and broken away, nor are the postero and antero lateral 

 borders sufficiently preserved to show more than the projection of 

 the basal rim beyond the coronal limits, as obtains in both examples, 

 the borders gradually converging, coronal limits defined from the 

 basal rim by a shallow sulcus ; the inner margin is broadly rounded, 

 with a slight sigmoidal curvature in passing from the obtuse anterior 

 angle to the slightly produced posterior angle. The crown surface 

 gently rises from the antero-lateral border, culminating in a broad 

 low crest situate in the posterior half of the coronal area, . thence 

 more steeply sloping into the narrow shallow concavity parallel 

 with the posterior border ; surface minutely punctate. Greatest 

 diameter across the inner margin .17 mm. ; length along the antero- 

 lateral border 7.5 mm. 



The type specimen shows a faint longitudinal depression near the 

 median line, which does not appear to have been produced by wear 

 as it descends to the unworn enameled inner margin, and toward 

 the antero-lateral border the surface is marked by a thread-like 

 groove, defining a narrow plain belt along that side, which is appa- 

 rently also a permanent constituent of the coronal contour. 



Another and smaller tooth belonging to the left ramus of the 

 lower jaw, shows nearly the same outline as the specimen described 

 above, but it is distinguished by the greater prominence of the 



