VERTEBRATES. 259 



sists in the diminutive proportions of the Kinderhook teeth as contras- 

 ted with the large dimensions attained by the Burlington and Keokuk 

 form, while in some minor respects the present form bears even closer 

 resemblance to the forms of the same group occurring in the St. Louis 

 and Chester divisions, and which is especially noticeable in the exceed- 

 ing delicacy of the coronal striation and the nearly perfect symmetry 

 in the proportions. 



It is worthy of remark that the largest individuals of the form under 

 consideration occur in the second or upper fish-bed of the Kinderhook 

 division, but these scarcely exceed the smallest examples of C. micropus, 

 while they present readily appreciable characters by which they maybe 

 recognized from that form in all its stages : The strife are uniformly 

 more numerous and crowded than in G. micropus, being also less diver- 

 gent laterally in the median cone in front ; similar differences are 

 observed in the inner face of the coronal cusps, where the striation is 

 conspicuously coarser and more sparce than in the present form. Com- 

 pared with G. politus, ~N. and W., of the Chester division, the same dif- 

 ferences are observed ; while the more frequent occurrence of a third 

 small accessory denticle exterior to the larger pair of lateral cones 

 (though this feature also obtains in G. micropus,) exhibit additional 

 distinctive characters : in G. exilis, whenever a third denticle makes its 

 appearance, it is apparently always developed in the angle at the base 

 of the median cone and first lateral denticle. There is, however, con- 

 siderable diversity in the teeth referred to G. microjms, and until it is 

 well understood, in connection with those forms which appear in later 

 deposits of the same period, we may not be able to determine the exact 

 relationship of these various forms. 



Geological position and locality : Not uncommon in both ichthyic 

 horizons in the Kinderhook division ; Burlington, Iowa. 



Cladodtjs Springeri, St. J. and W. 



pi. 2, rig. i-i3. 



Teeth attain medium size; base strong, subelliptical in outline, 

 broadly and more or less regularly rounded behind ; anterior border 

 gently arched, rarely even faintly sinuose, rounded at the obtuse lateral 

 extremities, gently inbeveled and produced below in a strong median 

 prominence of somewhat variable extent, but usually about one-third 

 the lateral diameter of the base, laterally defined, and sloping to the 

 moderately concave inferior surface, which is bordered by a more or 

 less distinct beveled area along the obtuse posterior margin, postero- 

 superior surface gently convex, and surmounted by a strong, roughened 

 prominence, which closely borders and conforms to the posterior margin, 



