﻿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 
  defined 
  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. 
  ? 
  

  

  PL 
  IV, 
  Fig. 
  15, 
  16. 
  

  

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

   orspatulate 
  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 
  interiorly. 
  Coronal 
  region 
  

   presenting 
  a 
  low 
  prominence, 
  the 
  obscurely 
  defined 
  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 
  closelv 
  punctate, 
  the 
  punctse 
  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 
  defined 
  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. 
  

  

  