172 PALEONTOLOGY OF ILLINOIS. 



Enniskillen, for the opportunity to examine sketches of the two 

 forms of the type species, from the Mountain limestone of Bristol, 

 England, belonging to the Museum at Florence Court, which, so far 

 as relates to general outline and coronal contour,- convey a tolerably 

 distinct impression of the peculiarities distinguishing the genus. 



The latter sketches exhibit examples of two forms, the one and 

 apparently that occurring most abundantly, represents an elongate 

 tooth below medium size, trapezoidal in outline, with very gradually 

 converging lateral borders, and moderate convexity from within out- 

 ward. The straight or antero-lateral border presents an abrupt face 

 with a sharp angulation above, and which seems to be enveloped 

 by an enamel belt; the oblique border appears to be denned by a 

 narrow rounded enamel fold inbeveled to the basal rim, which 

 expands somewhat beyond the limits of the coronal border, termi- 

 nating in the subacute posterior angle ; the inner margin is appa- 

 rently very gently, sigmoidally curved between the obtuse anterior 

 angle and the posterior extremity, or nearly at right angles with 

 the antero-lateral border. The crown shows moderate transverse 

 convexity of the principal prominence along the straight border, the 

 slope somewhat steeply descending into the posterior depression, 

 which is bordered by the narrow upraised alation. The second form 

 of teeth alluded to under the same specific designation, is repre- 

 sented by medium-sized examples, trigonal in outline, and strongly 

 arched longitudinally. The antero-lateral or straight border is 

 abruptly truncated, apparently vertical, and bordered by a belt of 

 coronal enamel, basal rim not clearly definable; the oblique border 

 is gently curved, rapidly converging toward the outer extremity, 

 character of enamel fold and basal rim not discernible; inner mar- 

 gin broadly and regularly arched between the inner angles, appa- 

 rently nearly at right angles with the straight border. Coronal 

 region occupied by the very prominent anterior ridge, which forms 

 a slight convexity extending from the sharp angulation along the 

 straight border posteriorly over two-thirds and more of the trans- 

 verse area of the crown, where the slope abruptly descends to the 

 oblique postero-lateral border, which shows a very narrow, obscurely 

 defined alation. In both of the forms above noticed the coronal 

 surface is minutely punctate, the punctae not arranged along distinct 

 transverse lines. A specimen of the narrow elongate form measures 

 in length along the straight border about 17 mm. ; breadth across 

 the inner margin 11 mm. ; lateral borders converge toward the outer 



