272 PALAEONTOLOGY OF ILLINOIS. 



they resemble in form, though perhaps less compressed, the external 

 pair about one-fifth the Light of the median coiie ; the outer face of 

 the principal cone is faintly ornamented by a few diverging tint ad- 

 like striae which rise in the triangular depression, dispersed and becom- 

 ing obsolete in the middle region of the cone — the lateral portions 

 and denticles apparently quite smooth and pulished. The basal portion 

 is not well exhibited, as also the posterior aspect of the crown, gently 

 arched vertically, anterior border gently siuuose, apparently uninter- 

 rupted, slightly produced, anterior basal angles inconspicuous, and 

 gently rounded into the slightly produced lateral extremities. Greatest 

 hight of tooth .30 inch, lateral diameter of base .45 inch. 



The unique example before us differs from its associates in the same 

 horizon in the sparseness of tLe coronal striaa and the compressed con- 

 dition of the principal cusp. Iu general outline it agrees intimately 

 with the teeth which we have provisionally recognized under the name 

 (J. Keokuk from the same horizon, of which rare form it may possibly 

 prove to be a much abraded example. But the imperfect condition of 

 the lateral portions of the original specimens of the latter form prevents 

 a critical comparison, and in view of the very strong vertical ridges 

 with which the principal cusp of that form -is ornamented, the tangible 

 differences seem sufficient to raise a doubt as to its specific identity 

 with the present form. 



Position and locality : Upper fish-bed of the Keokuk limestone ; 

 Keokuk, Iowa. 



Cladodtjs eccenteictts, St. J. and W. 



PI. i, Fig. 4. 



There occurs in the St. Louis limestone a form of which comparatively 

 few representatives have been found up to the present time, and these, 

 with one exception, are not in a sufficiently perfect state of preservation 

 to answer the purpose of an exhaustive comparison with allied forms. 

 Of the latter Messrs. Newberey aud Worthen have described a form 

 from the Chester limestone, C.politus, with which the present teeth bear 

 the most intimate resemblance, if indeed they prove not to be specifically 

 distinct. Perfect examples of C. politus are beautifully striated with 

 thread-like s'rise, precisely in the same manner as in the present teeth, 

 and which also recalls G. Fulleri of the Coal Measures. But among the 

 teeth under consideration, a single and elegantly preserved specimen, 

 which was obtained by Prof. Woethen at St. Louis, exhibits characters 

 which, if they prove not to be abnormal, render its reference to the 

 Chester form exceedingly improbable. The tooth in question is distin- 

 guished by the somewhat eccentric proportions of the base, which is 



