﻿15G 
  PALAEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  in 
  the 
  National 
  museum, 
  ;it 
  Washington, 
  the 
  loan 
  of 
  which, 
  for 
  ex- 
  

   amination, 
  was 
  kindly 
  procured 
  us 
  by 
  J'r. 
  Chari.kk 
  A. 
  White. 
  

  

  Geological 
  position 
  and 
  locality: 
  Carboniferous 
  limestone, 
  probably 
  

   of 
  the 
  age 
  of 
  the 
  Coal 
  Measures; 
  Grand 
  canon 
  of 
  the 
  Colorado, 
  I 
  tali 
  

   territory. 
  

  

  Deltodus 
  pbopinquub, 
  St. 
  J. 
  and 
  W. 
  

  

  P). 
  X. 
  Fir. 
  :i. 
  4. 
  

  

  Mandibular 
  posterior 
  teeth 
  sub-trigonal 
  or 
  Bub-spatulate 
  in 
  outline, 
  

  

  rather 
  strongly 
  arched 
  longitudinally, 
  with 
  Blight, 
  spiral 
  inrollmeut. 
  

   Anterodateral 
  border 
  sigmoidally 
  curved, 
  strongly 
  inbeveled, 
  an 
  

   copied 
  by 
  a 
  wide 
  enamel 
  fold, 
  which 
  is 
  sharply 
  defined 
  by 
  ad 
  

   narrow 
  furrow 
  from 
  the 
  extremely 
  narrow 
  basal 
  rim 
  ; 
  postero-lateral 
  

   border 
  converging, 
  at 
  an 
  angle 
  of 
  35- 
  more 
  or 
  less, 
  to 
  the 
  op] 
  

   border, 
  also 
  gently 
  curved, 
  coronal 
  enamel 
  forming 
  a 
  prominent, 
  

   rounded 
  fold, 
  inbeveled 
  to 
  the 
  sulcated, 
  moderately 
  deep 
  basal 
  rim, 
  

   which 
  was 
  apparently 
  continued 
  posteriorly 
  into 
  a 
  spur-like 
  angle: 
  

   inner 
  margin 
  sigmoidally 
  curved, 
  broadly 
  arched 
  around 
  the 
  bi 
  

   the 
  coronal 
  prominence, 
  in 
  breadth 
  exceeding 
  the 
  length 
  of 
  the 
  an- 
  

   terior 
  articular 
  border, 
  inferiorly 
  inbeveled. 
  Coronal 
  prominence 
  

   cupying 
  three-fourths 
  of 
  the 
  area, 
  rather 
  strongly 
  com. 
  x 
  laterally, 
  

   broadly 
  rounded 
  along 
  the 
  crest, 
  which 
  lies 
  a 
  little 
  anterior 
  of 
  the 
  

   median 
  line, 
  the 
  wide 
  anterior 
  slope 
  rounded 
  into 
  the 
  anterior 
  border. 
  

   posteriorly 
  steeply 
  inclined 
  into 
  the 
  narrow 
  depression 
  on 
  that 
  Bide, 
  

   defined 
  along 
  the 
  posterior 
  border 
  by 
  the 
  narrow, 
  rounded, 
  mod- 
  

   erately-upraised 
  alate 
  lobe. 
  Coronal 
  surface 
  traversed 
  by 
  rather 
  

   strong, 
  irregularly-spaced, 
  transverse 
  undulations 
  and 
  Longitudinally 
  

   marked 
  by 
  less 
  distinct 
  plications; 
  the 
  dense, 
  polished 
  enamel 
  also 
  

  

  nts 
  a 
  delicate 
  rugose 
  appearance, 
  the 
  minute 
  rUgS 
  having 
  ft 
  

  

  Longitudinal 
  direction; 
  worn 
  surfaces 
  over 
  the 
  outer 
  portion 
  of 
  the 
  

  

  crown 
  reveal 
  the 
  usual 
  pitted 
  structure, 
  the 
  punotSB 
  becoming 
  con- 
  

  

  ilueiit. 
  or 
  usually 
  Longitudinally 
  elongated 
  in 
  the 
  hollows 
  of 
  the 
  

   transverse 
  undulations. 
  A 
  ' 
  itb 
  shows 
  a 
  transverse 
  dian 
  

  

  across 
  the 
  inner 
  margin 
  of 
  86 
  nun 
  ; 
  Length 
  of 
  anterior 
  articular 
  I 
  

   bom 
  the 
  obtuse 
  inner 
  angle 
  to 
  the 
  point 
  of 
  LnroUment, 
  about 
  -J7 
  mm. 
  

  

  Mandibular 
  median 
  form 
  known 
  only 
  from 
  a 
  couple 
  of 
  fra 
  

   too 
  imperfed 
  for 
  figuring. 
  I; 
  La 
  chars 
  by 
  th< 
  promin 
  

  

  of 
  the 
  anterior 
  Lobe, 
  which 
  presents 
  a 
  rounded 
  ores! 
  defined 
  

   side 
  by 
  exceedingly 
  abrupt 
  declivities, 
  on 
  the 
  one 
  hand 
  descending 
  

   to 
  the 
  anterior 
  border 
  which 
  is 
  margined 
  by 
  an 
  obscurely 
  defined 
  

   iw 
  fold 
  strongly 
  inbeveled 
  to 
  the 
  deeply-ohanneled 
  basal 
  run. 
  

  

  