VERTEBRATES. 105 



the mandibular median teeth of Sandalodus, etc. They are, how- 

 ever, in this case distinguishable by the abrupt posterior declivity 

 of the coronal prominence and its distinctly denned border fold of 

 that side. 



Geological position and localities: Upper Burlington fish-bed ; Bur- 

 lington, Buffington Creek, Augusta, Pleasant Grove, Iowa ; Quincy, 

 Honey Creek, Henderson county, Illinois. 



STENOPTERODUS, sp. ? 



PI. IV, Fig. 15, 16. 



Posterior form of the upper jaw below medium-size, sub-elliptical 

 or spatulate in outline, moderately arched, longitudinally and strongly 

 inrolled along the outer margin. Antero-lateral border compara- 

 tively short, with slight obliquity outward and forward; postero-lat- 

 eral border gently arched, and rapidly converging from the acutely 

 rounded posterior extremity toward point of inrollment, making an 

 angle of 30, more or less, with the anterior border; inner margin 

 gently and regularly arched, inbeveled inferiorly. Coronal region 

 presenting a low prominence, the obscurely denned axis culminat- 

 ing about the middle of the tooth, flanked on one side by the wide, 

 nearly plane slope descending to the postero-lateral border, on the 

 other by a narrower, perceptibly steeper declivity, which merges 

 into the relatively narrow, plane anterior neck. Surface minutely 

 and closely punctate, the puncta showing quite regular disposition 

 in parallel longitudinal lines. Breadth across inner margin 14 mm. ; 

 length of antero-lateral border about 4.5 mm. Mandibular posterior 

 tooth proportionately corresponding with the opposed maxillary 

 form, trapezoidal in outline, rather strongly arched and inrolled. 

 Inner margin somewhat strongly arched round the base of the cor- 

 onal prominence, moderately so to the anterior angle, and slightly 

 concave in passing the posterior depression toward the extreme 

 angle; lateral borders not definable. The coronal ridge is strongly 

 convex transversely, occupying apparently quite half the lateral area 

 of the crown, posterior depression well marked and regularly con- 

 cave transversely, the anterior belt denned by a faint angulation, 

 apparently plain. Surface punctation precisely as observed in 

 connection with the maxillary posterior form, the punctse being 

 slightly compressed laterally, emphasizing the linear longitudinal 

 arrangement. 



