? 



VERTEBRATES. 



the point of inrollment and the sharply rounded posterior extremity, 

 the basal portion extending considerably beyond the limits of the 

 crown forming a thin marginal rim posteriorly ; inner margin broadly 

 arched in general course, suddenly constricted in front of the pos- 

 terior lobe, and thence more gently arched to the anterior angle. 

 Coronal region presents strong contour contrasts, posterior lobe 

 prominent, constituting somewhat more than half the lateral diam- 

 eter of the tooth, abruptly rising in front into the rounded crest 

 from which the slope in the opposite direction gently descends in 

 slight transverse convexity to the postero-lateral border, where the. 

 coronal enamel forms a thick inbeveled fold distinctly defined from 

 the basal portion ; the anterior neck is separated from the posterior 

 prominence by a deep narrow depression, in well-preserved exam- 

 ples showing a distinct narrow secondary ridge with steep declivity 

 bordering the median depression, a transversely more gently convex 

 wider belt intervening between the latter and the shallow furrow 

 defining the posterior limits of the narrow relatively prominent belt 

 along the antero-lateral border, where the coronal enamel forms a 

 well-marked fold inbeveled to the basal portion. Superficial punc- 

 tation the same as in the opposed mandibular teeth. A mature 

 tooth measures in greatest diameter of crown at the inner margin, 

 22.5 mm., the basal portion being considerably farther prolonged 

 into the posterior spur ; length of antero-lateral border to point of 

 inrollment, 8 mm. ; median furrow at inner margin, 13 mm. distant 

 from posterior extremity. 



Associated with the above described forms, the collections contain 

 a few examples of Helodus-\ike teeth, mostly isolated individuals, but 

 occasionally in series, which we are inclined to identify with the 

 present species. One of these series, in the collection of Professor 

 Worthen, presents a series of four teeth firmly soldered at the im- 

 pingement of their bases, without visible suture, forming a deltoid 

 figure, belonging to the right ramus of the upper jaw. The three 

 outer teeth regularly and gradually diminish in size from behind 

 outward, .except the innermost one, which presents the usual condi- 

 tion of immature coronal ridge apparently resting upon the inner 

 deep basal border of the immediately preceding tooth. The anterior 

 basal margin of the outer tooth is channeled, the coronal ridge of 

 /ill the individual teeth rises into a turgid sub-median apex nearest 

 the postero-lateral border of the series, slightly concave along the 

 sloping obtuse crest on either side and sharply deflected forward at 

 the extremities into a sort of short fold ; the inner margin is gently 



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