266 PALAEONTOLOGY OF ILLINOIS. 



ally ami beveled to the inferior surface ; inferior surface nearly plain 

 or gently excavated, with a narrow beveled belt along the greater por. 

 1 ion of the posterior margin; postero superior surface moderately con- 

 vex, occupied nearly centrally by a sharply denned, linear prominence, 

 in lateral extent nearly equal to half the diameter of the base. Coronal 

 portion slightly constricted along the basal line in front, gently depressed 

 at the base of the principal cone, which latter is very strong, vertical 

 to the horizontal piano of the base or slightly recurved sigmoidallyi 

 more or less laterally deflected, or erect, gently convex in front, strongly 

 arched behind, lateral margin compressed, sharp and gradually con. 

 verging to the acute apex; lateral denticles normally four on either 

 extremity, alternately arranged in pairs, sometimes with delicate nidi 

 nieutary denticles appearing in the angles of the persistent ones, exte. 

 rior pair more or less divergent and recurved, similar in shape to 

 the median cone, though less compressed in front; coronal surface 

 ornamented with sharp, threadlike, regularly arranged costa?, which, 

 in the median cone seldom reach more than half the distance to the 

 apex in front, with rather a wide plain space bordering the margin in 

 which the lateral costse become obsolete; in the lateral denticles the 

 costre are very similar but less numerous, and extend nearly to the 

 apices ; in the posterior face they are equally regular in disposition, but 

 more numerous and delicate. A specimen of ordinary size measures in 

 greatest diameter of base .28 inch, anteroposterior diameter .13, greatest 

 bight of tooth .32 ; a smaller tooth of greater lateral diameter is .IS inch 

 in lateral diameter, lesser diameter .08, hight about .15 inch. 



This beautiful little form is represented by a tine series of specimens 

 in the collections of Messrs. Wachsmuth and Speinger, which exhibit 

 remarkable persistency in the distinctive characteristics, and which, in 

 well preserved specimens, readily enable their determination. The 

 form is most intimately allied to G. Springeri, with which it is associated ; 

 but, as has been shown in connection with the observation on that form? 

 the present are not to be confounded with the minute and worn exam, 

 pies of the above form which they most resemble in outline, but from 

 which they are distinguished by the greater lateral extent of the anterior 

 basal ridge, the shallow mesial .depression, the finer and more regular 

 costation, and absence of accessory spinose processes along the anterior 

 ba:-al border of the crown. 



Position and locality : The earlier and most numerous acquisitions of 

 Mr. Speinger are from the lower fish-bed of the Kinderhook, but Mr. 

 Waciismtjth has obtained a few specimens from the upper tish bed of 

 the same formation, which are uudistinguishable from the earlier teeth ; 

 Burlington, Iowa. 



