﻿VEBTEBBATES. 
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  a 
  line 
  connecting 
  the 
  angles 
  of 
  the 
  inner 
  margin, 
  or 
  very 
  slightly- 
  

   oblique 
  in 
  its 
  forward 
  and 
  outward 
  course, 
  the 
  coronal 
  enamel 
  form- 
  

   ing 
  a 
  shallow 
  fold 
  inbeveled 
  to 
  the 
  channeled 
  basal 
  portion 
  ; 
  postero- 
  

   lateral 
  border 
  not 
  shown 
  ; 
  inner 
  margin 
  produced 
  obliquely 
  backward 
  

   and 
  rather 
  sharply 
  rounded 
  at 
  the 
  base 
  of 
  the 
  coronal 
  ridge, 
  thence 
  

   making 
  a 
  concave 
  curvature 
  to 
  the 
  acute 
  posterior 
  extremity. 
  Cor- 
  

   onal 
  ridge 
  nearly 
  median, 
  culminating 
  in 
  a 
  rounded 
  crest, 
  posterior 
  

   slope 
  abrupt 
  to 
  the 
  depression 
  on 
  that 
  side, 
  whence 
  steeply 
  rises 
  

   the 
  posterior 
  alation, 
  also 
  steeply 
  sloped 
  in 
  front 
  and 
  defined 
  by 
  a 
  

   faint 
  angulation 
  from 
  the 
  relatively 
  plain 
  belt 
  occupying 
  the 
  anterior 
  

   portion 
  of 
  the 
  crown, 
  and 
  which 
  is 
  apparently 
  destitute 
  of 
  longi- 
  

   tudinal 
  furrows 
  or 
  transverse 
  rugae. 
  Coronal 
  surface 
  regularly 
  and 
  

   closely 
  punctate. 
  Transverse 
  diameter 
  across 
  the 
  inner 
  margin 
  15.5 
  

   mm. 
  ; 
  length 
  along 
  antero-lateral 
  border 
  9.5 
  mm. 
  

  

  The 
  above 
  description 
  is 
  based 
  upon 
  a 
  single 
  imperfect 
  specimen 
  

   derived 
  from 
  the 
  Lower 
  Burlington 
  limestone, 
  and 
  which 
  is 
  the 
  

   earliest 
  discovered 
  representative 
  of 
  the 
  genus. 
  The 
  somewhat 
  dis- 
  

   tinct 
  demarkation 
  of 
  the 
  plain 
  anterior 
  area 
  of 
  the 
  crown 
  offers 
  a 
  

   character 
  recalling 
  typical 
  Cochliodus, 
  its 
  relative 
  great 
  breadth 
  con- 
  

   stituting 
  the 
  chief 
  distinguishing 
  feature 
  ; 
  on 
  the 
  other 
  hand, 
  the 
  

   coronal 
  contour 
  is 
  remarkably 
  similar 
  to 
  that 
  ascribed 
  to 
  Chitonodus, 
  

   of 
  which 
  we 
  believe 
  it 
  to 
  be 
  a 
  worn 
  example. 
  Its 
  relations 
  to 
  the 
  

   species 
  so 
  well 
  represented 
  in 
  the 
  collections 
  from 
  the 
  next 
  succeed- 
  

   ing, 
  or 
  Upper 
  Burlington 
  deposits 
  cannot 
  be 
  fully 
  determined 
  ; 
  but 
  

   the 
  before-mentioned 
  marked 
  definition 
  of 
  the 
  coronal 
  ridge 
  from 
  the 
  

   plain 
  belt 
  in 
  front 
  presents 
  a 
  striking 
  contrast 
  in 
  contour 
  with 
  the 
  

   same 
  form 
  of 
  C. 
  Springeri. 
  Not 
  even 
  worn 
  examples 
  of 
  the 
  latter 
  

   species, 
  in 
  which 
  the 
  transverse 
  and 
  even 
  the 
  longitudinal 
  folds 
  are 
  

   obliterated, 
  bear 
  any 
  intimate 
  resemblance 
  in 
  the 
  particulars 
  alluded 
  

   to 
  as 
  characteristic 
  of 
  the 
  present 
  tooth. 
  

  

  Geological 
  position 
  and 
  locality 
  : 
  Lower 
  Burlington 
  limestone 
  ; 
  

   Burlington, 
  Iowa. 
  

  

  Chitonodus 
  teibulis, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  VII, 
  Fig. 
  18-21. 
  

  

  Teeth 
  of 
  medium 
  size, 
  of 
  which 
  representatives 
  of 
  the 
  mandibular 
  

   and 
  maxillary 
  posterior 
  forms 
  alone 
  are 
  known. 
  

  

  Posterior 
  teeth 
  of 
  the 
  maxillaries 
  presenting 
  the 
  usual 
  sub-quad- 
  

   rilateral 
  outline, 
  strongly 
  arched 
  and 
  inrolled 
  along 
  the 
  outer 
  margin. 
  

   Antero-lateral 
  border 
  forming 
  nearly 
  a 
  right 
  angle/ 
  with 
  a 
  direct 
  

  

  