VERTEBRATES. 261 



at the same time, even the lateral denticles themselves have been sub- 

 jected to partial, and sometimes in the case of the more delicate ones, 

 total obliteration. Denuded of their distinctive characteristics, these 

 teeth scarcely present a suggestion of their real specific identity, while 

 amongst themselves they are even more diverse than the greatest 

 extremes exhibited by well expressed examples. Yet we have observed 

 in these smaller teeth variations in the number of true lateral denticles, 

 which indicate that in this respect there was not absolute uniformity. 

 In some of the normal examples one extremity may bear an extra den- 

 ticle, in others there may be one or two denticles wanting. And in 

 abnormally (?) developed teeth, as also in specimens which have suffered 

 most from abrading agencies, there may occur but two and three den- 

 ticles on either extremity, or but a single one on one and a pair or three 

 denticles upon the opposite extremity. Amongst the more minute 

 examples teeth less than .15 of an inch in lateral diameter, and larger, 

 the median cone often presents a coarse costation quite in contrast to 

 that ordinarily presented, and which has led to the conclusion that the 

 forms exhibiting this feature never belonged to the rows constituted by 

 the larger teeth, but pertain either to the anterior or posterior portions 

 of the jaws. 



The teeth referable to the form above described have some general 

 resemblance to G. succinctus, of the fish-bed next above the horizon 

 whence these were derived; but even a cursory comparison will at once 

 reveal the wide distinctions between them, as exhibited in the basal 

 region, and the fine costation of the median cone. The worn examples 

 also resemble C. alternatus of the same horizon — a smaller and more 

 symmetrical form, destitute of accessory processes, and otherwise well 

 marked specifically, as shown in the illustrations of PI. II, in which 

 both forms are represented. 



It affords us pleasure to associate the name of our friend Mr. Springer 

 with this fine form, as a slight token of our appreciation of the valuable 

 aids he has contributed to this work. 



Position and locality: Lower fish-bed of the Kinderhook formation; 

 Burlington, Iowa. 



Cladodtjs exigrjus, St. J. and W. 



PI. 3, Fig. 13-15. 



Teeth of small size, though rather stoutly fashioned. Base long, or 

 subelliptical in general outline, extremities obtusely rounded, slightly 

 sinuous in front, and arched ; moderately excavated below, and gently 

 beveled along the posterior margin, the exterior mesial ridge occupying- 

 two-thirds or more of the lateral diameter of the base, and forming a 



