260 PALEONTOLOGY OF ILLINOIS. 



widely spaced from the base of tbe crown, and of variable lateral extent, 

 in this respect apparently conforming to the distance between the 

 obscure marginal angles, hence in laterally elongated bases it is of pro- 

 portionately greater lateral extent than in more abbreviated individuals, 

 as represented by the small teeth, in which it is reduced to a strong 

 pad-like prominence scarcely one-fourth the greatest diameter of the 

 base. To some extent the same is true of the anterior basal ridges, 

 though in some examples it assumes the condition, but without the dis- 

 tinct definition, of the median ridge in the larger teeth, or those which 

 present the normal aspect of the form. In well-preserved specimens 

 there is less variability in the coronal region than remarked in the basal 

 portion, the crown nominally presenting a strong median cone flanked 

 on either hand by four pairs of lateral denticles alternating in size, the 

 exterior pair stout, moderately deflected laterally, and recurved at an 

 angle greater than the median cone, which they resemble in shape, per- 

 haps less symmetrical ; the median cone gradually tapers to the acute 

 apex, sublenticular in transverse section, gently convex in front, strongly 

 arched posteriorly, with sharp lateral edges, compressed or faintly 

 depressed at the base in front, and marked with more or less closely 

 and somewhat irregularly arranged angular costse, which bifurcate 

 descending, with intercalated cost£e above, and which ascend half or 

 two-thirds the distance to the apex in front ; in the posterior face they 

 are more delicate and more closely crowded or numerous ; in front the 

 costse terminate in slight basal knobs, probably the worn bases of 

 accessory processes, and which appear in the lateral extremities, often 

 forming a dense border of spinose processes encircling the anterior 

 border of the crown, and flanking the base of the exterior denticles ; 

 the lateral denticles are similarly striated in the anterior face, a few 

 strong, sharp ridges terminating in the apex, the posterior face occupied 

 by delicate thread-like ridges. 



The form under consideration is the most numerously represented of 

 the Kinderhcok Cladodi, the original collection of Mr. Springer offering 

 the means of a comprehensive study of the form under the varied 

 aspects which it displays, and which, but for this extensive material, 

 would lead to serious misconception of the character presented by the 

 widely diverse individuals of which it is composed. In selecting mate- 

 rial for illustration, we have aimed not so much at giving a graduated 

 series, as to illustrate by a few well chosen examples the variable char- 

 acter of individuals of various sizes, positions, and conditions of preser- 

 vation. Perhaps the most marked variableness is directly attributable 

 to abrasion, by which, especially in the smaller teeth, the spinose pro- 

 cesses at the base of the crown have suffered most, in the majority of 

 the teeth there remaining scarcely a vestige of these processes, while, 



