302 PALAEONTOLOGY OF ILLINOIS. 



fully marked with delicate ridges radiating from the apex to about the 

 middle, where they are interrupted and deflected, or replaced by inter- 

 calated ridges, ■which are gathered iu an elegant reticulated border at 

 the base of the inner face, a slight mesial ridge ascending the outer 

 face of the great cone, giving off at intervals a few lateral secondary 

 ridges. A somewhat smaller variety, in position probably anterior to 

 the teeth just described, varying from .15 to .5 inch in length, are 

 recognized by their more strongly arched outline, the lateral wings 

 often anteriorly deflected, root narrower and less obliquely produced 

 along the inner margin, central cone relatively larger, and the denticu- 

 lations of the lateral crests decreasing in number with the abbreviation 

 of the lateral wings — otherwise presenting no marked contrast with the 

 large median teeth. In the perfect condition the crown is enveloped in 

 a firm, polished enaniel-like layer, a fine punctation appearing in worn 

 surfaces. 



In general outline the present form is somewhat like 0. elegantuhis, 

 N. and TY, of the Upper Burlington limestone, although a direct com- 

 parison of the two forms discovers differences which widely distinguish 

 them specifically, as remarked in the details of coronal sculpturing, 

 which is much more delicately wrought. The dentition presents a simi- 

 lar range of variation observed in the above and other species, while 

 the persistency of the specific characteristics readily affords the means 

 of identifying the isolated teeth from various parts of the jaws. 



Position and locality : Common in the lower fish-bed of the Kinder- 

 hook ; Burlington, Iowa. 



Orodtts major, St. J. and W. 



pi. vn, Kg. 10. 



Teeth of large size, strong, symmetrical proportions. Lateral diame- 

 ter of base equal to that of the crown, in depth exceeding the general 

 elevation of the crown, but narrower, massive, moderately oblique, pos- 

 terior angles sharply rounded, posterior face gently arched in both 

 directions, with a more or less marked depression parallel with and just 

 beneath the coronal border, anterior face moderately and broadly exca- 

 vated, the shoulder beneath the coronal margin apparently obscurely 

 defined, inferior surface gently arched vertically, and moderately bev- 

 eled to the obtuse posterior margin, anterior and posterior surfaces 

 coarsely roughened or pitted. Crown gently and regularly arched 

 between the extremities, which latter are more or less curved forward, 

 rising into a strong, obtusely conical median cone, which is somewhat 

 strongly produced before and behind, and broadly rounded, rapidly 

 narrowed to the nearly linear lateral extensions, which are abruptly 



