402 PALAEONTOLOGY OF ILLINOIS. 



form C. serratus, Agassiz. It differs, however, from that form by readily 

 distinguishable peculiarities, as the less robust proportions of the crown, 

 more obtusely acuminate apex, and the stronger and fewer serrations 

 of the crest, narrower basal band in the concave face, and the less 

 strongly though more broadly arched basal margin of the convex face. 

 Position and locality : From a stratum of limestone overlying a thin 

 bed of coal near the base of the lower Coal Measures ; Fort Dodge, 

 Iowa. 



Gesus PKISTODTTS, Agassiz. 

 Pristodus? actjmtnattjs, St. J. and W. 



PI. X A, Fig. 6. 



We have provisionally referred to the genus Pristodus, of Agassiz, a 

 minute form represented by a unique example in the collection of Mr # 

 Springer, which possess distinctive features which seem to indicate a 

 more intimate relationship with that genus than with any other group 

 of teeth known in the American Carboniferous deposits. The tooth is 

 distinguished by its lateral elongation and comparatively thin or com- 

 pressed crown, which is slightly curved backward, sharply rounded at 

 the extremities, basal border sharply iubeveled behind and defined along 

 the line of the superior coronal region by au obtusely produced basal 

 ridge, gently arched vertically, crest strongly denticulated and rising 

 into a strong, laterally deflected, eccentric median prominence, the den- 

 ticulations very similar throughout, though gradually and more or less 

 regularly diminishing in size laterally, in shape lanceolate terminating 

 in an acute apex, and defined by relatively well-marked vertical sulci, 

 which descend nearly to the produced basal angle; posterior (?) face 

 faintly convex vertically, though slightly expanded on nearing the basal 

 border, the inbeveled portion being apparently occupied by a simple 

 coronal fold, anterior face gently concave in both directions, slightly 

 exceeding in hight the opposite face, sharply inbeveled along the base ; 

 both faces smooth and polished. Lateral diameter of tooth .09 inch, 

 greatest hight of crown .04. Base unknown. 



The exceedingly delicate little tooth above noticed, unfortunately, 

 reveals only one side of the crown in full, only a portion of the concave 

 face can be seen, and the base has either crumbled away, else it forms 

 so inconspicuous an object as to appear obsolete. The specimen pre- 

 sents peculiarities in coronal conformation which more closely resemble 

 the Pristodus falcatus, Agass., of the Yorkshire Carboniferous lime- 

 stone, than any of the forms with which it is associated or those occur- 

 ring in superimposed strata. Its basal region in the posterior face, 



