306 PALAEONTOLOGY OF ILLINOIS. 



same horizon; at the numerous exposures of the horizon in Louisa 

 and DesMoines counties, Iowa, Henderson county, Illinois. 



Orodtts fastigiatus, St. J. and W. 



pi. vi, rig. 1-3. 



Teeth small, robust, triangular iu general outline. Base very oblique 

 to the crown, thick, laterally expanded below, (in worn examples the 

 margins are quite parallel or rouuded) and slightly concave along the 

 lower edge, lateral diameter little greater than the vertical, posterior 

 face gently convex, opposite side more or less deeply excavated, with a 

 well defined shoulder parallel with the coronal margin, inferior surface 

 forming a rather wide, angular area, obliquely beveled to the posterior 

 edge. (Jrown inbeveled below and sharply defined from the base, 

 strongly arched vertically, rising into a high pyramidal prominence, 

 flanked by the lateral wings, which are sharp-crested and marked upon 

 either side by two or three angular vertical ridges which terminate 

 below in nodose prominences, sometimes bifurcated, meeting in the crest 

 where they sometimes produce obscure denticulations ; the median cone 

 is flanked in the outer face by a very strong, angular buttress, abruptly 

 descending and strongly produced towards the base, and ornamented 

 with lateral ridges similar to those occurring in the lateral wings, 

 besides being delicately marked with undulated ruga? ; the posterior 

 face of the crown is also occupied by an angular, though less prominent, 

 mesial ridge, which rises from a turgid basal prominence, and marked 

 above by delicate decussations similar to those observed in the sharp 

 crest of the lateral wings ; originally the crown was acutely pointed, 

 but in the larger number of specimens it is truncated, and in some 

 examples it is reduced to less than half the original elevation. The 

 coronal surfaces are uniformly enveloped iu a dense, highly polished 

 enamel-like coating. A specimen of ordinary size measures in greatest 

 lateral diameter .25 inch, greatest an tero posterior diameter of crown 

 .16, hight of tooth -.34 inch. 



The form here indicated is represented by numerous individuals in 

 the collections from the Upper Burlington fish-bed horizou, and withal 

 they present considerable individual variation, we have been unable to 

 trace their specific identity with other forms known from the same 

 localities. The peculiar form of the teeth strongly impresses one with 

 the belief that they occupied an anterior position upon the jaws. But 

 we know of no species whose median teeth can be satisfactorily identi- 

 fied with those under consideration, while they vary in size and in 

 certain coronal features among themselves to such an extent as appa- 

 rently to justify the conclusion that they are specifically distinct from 



