304 PALAEONTOLOGY OF ILLINOIS. 



Oeodus variocostatus, St. J. and W. 



PI. Vn, Fig. 1-9. 



Teeth ranging from small to above medium in size, presenting con- 

 siderable variation in form and coronal contour. Large teeth laterally 

 elongated, extremities more or less curved anteriorly, generally intequi- 

 lateral, gently arched vertically, Base moderately thick, more or less 

 oblique to the crown, moderately excavated in the outer face, superior 

 shoulder narrow but well-defined, posterior surface slightly arched in 

 both directions, both faces coarsely roughened, inferior surface smooth, 

 beveled to the obtuse posterior border in nearly the same horizontal 

 plane as the crown, posterolateral angles sharply rounded. Crown 

 produced into a median, or generally submedian, turgid, more or less 

 quadrangular or pyramidal, and often obtusely truncated cone, which 

 is protruded beyond the basal line in front and behind, and well-defined 

 from the lateral wings, which latter are also constricted basally, very 

 gradually tapering toward the extremities, which are broadly rounded, 

 and equal or slightly exceed the lateral extension of the base; the 

 crown is traversed by an irregular, tortuose, usually obscurely defined, 

 though sometimes sharply angular submedian crest, which is continued 

 nearly to the apex of the principal prominence in some individuals, 

 from which sharp or obtusely angular, very irregular and obliquely 

 deflected costse descend to the basal margins, where they often form 

 buttress like supports, flanked by faint secondary ridges or bifurcations, 

 which sometimes produce the appearance of rude basal folds; the 

 median prominence is surrounded by similar vertical plicte, which, how- 

 ever, become obsolete before reaching the upper third of the cone, except 

 the more or less prominent angular mesial ridge, which is generally 

 discernible in either face, and often continued to the apical extremity in 

 examples which have not been abraded; in some individuals the coronal 

 carinas present a vermiculose appearance, and are clustered at the base 

 of the median cone in an elegantly, though irregularly plicated belt. 

 Teeth possessing the above mentioned characters range in size from 

 those above one inch in lateral diameter to small forms not exceeding 

 one-fourth inch in length. With these more regular teeth there is found 

 a variety represented by smaller teeth, which are especially distinguish- 

 able by their abbreviated lateral extent, relatively greater antero- 

 posterior diameter, and depressed summit. In some of the latter teeth 

 the base is very strong and deep, and deeply excavated in the anterior 

 face, the crown strongly produced in front, and gently arched along the 

 posterior border, the median prominence very depressed, and occupying 

 the greater portion of the coronal area, lateral extremities bearing one 

 to three irregularly developed lobes, but in general appearance and 



