﻿VEBTEBBA.TES. 
  99 
  

  

  specifically. 
  The 
  mandibular 
  posterior 
  teeth 
  are 
  proportionately 
  

   shorter 
  from 
  within 
  outward 
  and 
  wider 
  across 
  the 
  inner 
  margin, 
  and 
  

   the 
  median-lobe 
  perhaps 
  less 
  well 
  defined 
  from 
  the 
  narrow 
  anterior 
  

   belt; 
  while 
  the 
  opposed 
  tooth 
  of 
  the 
  upper 
  jaw 
  has 
  the 
  secondary 
  

   lobe 
  relatively 
  much 
  more 
  strongly 
  developed 
  and 
  the 
  coronal 
  prom- 
  

   inence 
  occupying 
  a 
  greater 
  portion 
  of 
  the 
  crown 
  surface. 
  

  

  The 
  state 
  of 
  preservation 
  of 
  these 
  diminutive 
  teeth, 
  especially 
  in 
  

   the 
  instance 
  of 
  those 
  pertaining 
  to 
  the 
  mandible, 
  is 
  extraordinary. 
  

   But 
  of 
  the 
  maxillary 
  teeth 
  the 
  collections 
  afford 
  few 
  examples, 
  and 
  

   these 
  are 
  without 
  exception 
  mutilated 
  at 
  the 
  antero-lateral 
  border, 
  

   in 
  consequence 
  of 
  the 
  extreme 
  although 
  notMisproportionate 
  attenu- 
  

   ation 
  they 
  undergo 
  in 
  that 
  region. 
  

  

  Geological 
  position 
  and 
  localities 
  : 
  St. 
  Louis 
  limestone 
  ; 
  Alton 
  and 
  

   Monroe 
  county, 
  111. 
  ; 
  Pella, 
  Iowa 
  ; 
  St. 
  Louis, 
  Mo. 
  

  

  ■ 
  Deltoptychius 
  nitidus, 
  (Leidy, 
  sp.) 
  

  

  PI. 
  V, 
  Fig. 
  16. 
  

   Coohliodtts 
  nitidus, 
  Leidy, 
  1856. 
  Trans. 
  Am. 
  Phil. 
  Soc, 
  xi, 
  p. 
  87. 
  PL 
  v, 
  f. 
  2. 
  

  

  The 
  present 
  species 
  was 
  originally 
  described 
  by 
  Dr. 
  Leidy, 
  from 
  a 
  

   large-sized 
  specimen 
  of 
  the 
  posterior 
  tooth 
  of 
  the 
  left 
  ramus 
  of 
  

   the 
  lower 
  jaw, 
  which 
  was 
  obtained 
  at 
  Chester, 
  in 
  this 
  State. 
  The 
  

   teeth 
  are 
  massive, 
  and 
  strongly 
  built, 
  triangular 
  in 
  outline, 
  pos- 
  

   tero-lateral 
  border 
  rapidly 
  converging 
  toward 
  the 
  outer 
  extremity, 
  

   inner 
  margin 
  broadly 
  curved 
  round 
  the 
  base 
  of 
  the 
  median 
  prom- 
  

   inence, 
  antero-lateral 
  border 
  nearly 
  straight, 
  relatively 
  short, 
  the 
  

   enamel 
  fold 
  extending 
  well 
  down 
  over 
  the 
  abrupt 
  face. 
  The 
  basal 
  

   portion 
  along 
  the 
  postero-lateral 
  border, 
  in 
  a 
  mature 
  individual 
  like 
  

   the 
  type 
  noticed 
  by 
  Dr. 
  Leidy, 
  extends 
  in 
  a 
  conspicuous 
  rim 
  beyond 
  

   the 
  well-defined 
  enamel 
  fold, 
  terminating 
  in 
  a 
  strong, 
  bony 
  spur, 
  

   posteriorly, 
  and 
  reaching 
  the 
  point 
  of 
  strong 
  inrollment, 
  where 
  it 
  pre- 
  

   sents 
  the 
  usual 
  channeled 
  condition. 
  The 
  crown 
  is 
  strongly 
  arched 
  

   from 
  within 
  outward, 
  median 
  lobe 
  embracing 
  about 
  half 
  the 
  lateral 
  

   diameter 
  of 
  the 
  crown, 
  usually 
  prominently 
  arched 
  transversely, 
  a 
  

   slight 
  angulation 
  defining 
  it 
  from 
  the 
  narrow 
  anterior 
  belt, 
  the 
  slope 
  

   behind 
  descending 
  into 
  the 
  posterior 
  depression, 
  which 
  is 
  bordered 
  

   by 
  the 
  relatively 
  narrow 
  alation. 
  A 
  medium-sized 
  tooth 
  measures, 
  

   along 
  the 
  postero-lateral 
  border 
  from 
  the 
  posterior 
  angle 
  to 
  point 
  

   of 
  inrollment, 
  12 
  mm. 
  ; 
  length 
  along 
  antero-lateral 
  border, 
  7.5 
  

   mm. 
  ; 
  breadth 
  across 
  inner 
  margin, 
  10 
  mm. 
  

  

  The 
  collections 
  contain 
  examples 
  of 
  maxillary 
  posterior 
  teeth, 
  from 
  

   the 
  same 
  deposits 
  and 
  localities, 
  associated 
  with 
  the 
  above 
  described 
  

  

  