300 PALEONTOLOGY OF ILLINOIS. 



ornamentation of the coronal region bears somewhat close resemblance 

 to 0. major of the Lower Burlington limestone ; but in the latter form 

 the base is relatively narrower and of greater depth. They may also 

 be compared with the Keokuk form 0. carinaiits, from which it differs 

 in the relatively broad crown and obtusely angular crest. 



Geological position and locality : The specific designation is given in 

 honor of Dr. C. A. vY"HiTE,~by whom the unique specimen described 

 was found in the upper beds of the Kiuderhook formation ; Legrand, 

 Marshall county, Iowa. 



Orobus dectjssatus, St. J. and "W. 



PI. VI, Fig. 10-15. 



Teeth of small and medium size, attaining .75 inch in length, symme- 

 trical though somewhat variable in form, laterally elongated, vertically 

 arched, extremities slightly curved forward. Base comparatively shal- 

 low, especially in the large median teeth, oblique to the crown, beyond 

 the inner margin of which it is more or less strongly produced forming 

 a wide, linear area, with angular lateral extremities, inferior surface 

 smooth, beveled to the thin posterior edge, deeply channeled in front 

 with a more or less well defined angulation or shoulder parallel with the 

 coronal margin. The crown is moderately arched vertically, and pre- 

 sents a large median cone, more or less eccentric to the middle, flanked 

 by two to four smaller though well-marked denticulations in either 

 wing, which regularly and rapidly diminish in size toward the extremi- 

 ties, and which are ornamented, in the same manner as the principal 

 cone, by a few very strong, rather widely spaced ridges converging 

 towards the apices of the prominences, which latter are connected by a 

 more or less obscure coronal crest; the vertical ridges are quite regular 

 in the posterior face, but in the anterior, or more abrupt face, they 

 irregularly bifurcate descending, each bifurcation bearing the delicate 

 lateral decussations which constitute the peculiarly ornate characteris- 

 tics of the form. The anterior teeth are much smaller, base proportion- 

 ately deeper and narrower, generally more considerably arched, median 

 prominence strongly produced iuferiorly behind, lateral extremities 

 rapidly attenuated, contour and ornamentation similar to the median 

 teeth, with indications of basal plica?, and varying in length from .15 to .5 

 inch. Posterior teeth long, nearly linear, " depressed, crown slightly 

 arched, principal cone submedian, obtusely conical or scarcely distin- 

 guishable from the contiguous denticles, of which latter three or four 

 occur in one wing and probably one or two less in the opposite extrem- 

 ity, relatively large and radiatingly sculptured, as described above. 

 The median prominence is often truncated from wear, but in the perfect 



