﻿66 
  PALEONTOLOGY 
  OF 
  ILLINOIS. 
  

  

  While 
  it 
  is 
  not 
  deemed 
  improbable 
  that 
  the 
  acquisition 
  of 
  more 
  

   complete 
  evidence 
  may 
  lead 
  to 
  the 
  discovery 
  of 
  still 
  more 
  intimate 
  

   relationship 
  between 
  Psephodtu 
  and 
  typical 
  Coohliodonts, 
  the 
  rela- 
  

   tions 
  of 
  the 
  former 
  with 
  Paanvmodus 
  are 
  so 
  remote 
  as 
  to 
  preclude 
  

   the 
  inference, 
  which 
  has, 
  however, 
  found 
  expression, 
  that 
  Psepkodu* 
  

   constitutes 
  a 
  sort 
  of 
  transition 
  connecting 
  the 
  Psainmodonts 
  with 
  

   the 
  Cochliodonts. 
  

  

  Psephodus 
  obliquus, 
  St. 
  J. 
  and 
  W. 
  

  

  PL 
  I, 
  Fitf*. 
  1. 
  S. 
  3, 
  4. 
  5. 
  

  

  Under 
  the 
  above 
  term 
  are 
  included 
  series 
  of 
  teeth 
  represented 
  in 
  

   the 
  collections 
  by 
  a 
  number 
  of 
  individuals, 
  which 
  range 
  themselves 
  

   under 
  two, 
  perhaps 
  three 
  or 
  more 
  well-defined 
  groups, 
  distinguished 
  

   by 
  their 
  outline 
  and 
  general 
  conformation, 
  and 
  which, 
  taken 
  together, 
  

   are 
  not 
  considered 
  separable 
  into 
  so 
  many 
  distinct 
  species; 
  on 
  the 
  

   contrary, 
  there 
  exists 
  strong 
  presumptive 
  evidence 
  of 
  their 
  having 
  

   constituted 
  parts 
  of 
  the 
  dentition 
  of 
  one 
  and 
  the 
  same 
  specie 
  

   Only 
  the 
  two 
  most 
  conspicuous 
  forms 
  are 
  noticed 
  in 
  this 
  pla 
  

   One 
  of 
  these 
  forms 
  is 
  represented 
  by 
  teeth 
  which 
  possess 
  the 
  char- 
  

   acteristics 
  of 
  what 
  may 
  be 
  regarded 
  the 
  typical 
  representative 
  teeth 
  

   of 
  the 
  genus 
  Psephodus, 
  comparable 
  with 
  the 
  larger 
  and 
  more 
  tumid 
  

   teeth 
  of 
  P. 
  magmu, 
  Agass., 
  distinguishable, 
  however, 
  by 
  their 
  more 
  

   symmetrical 
  and 
  smaller 
  size. 
  In 
  general 
  outline 
  eonvolutely 
  and 
  

   irregularly 
  pentangular, 
  moderately 
  inrolled, 
  outer 
  extremity 
  slightly 
  

   rounded 
  and 
  obliquely 
  truncated 
  from 
  front 
  outward 
  and 
  downward, 
  

   the 
  1-asal 
  portion 
  showing 
  a 
  broad 
  channel 
  beneath 
  the 
  projecting 
  

   coronal 
  border; 
  anterior 
  border 
  slightly 
  sigmoidnlly 
  curved, 
  forming 
  

   nearly 
  a 
  right 
  angle 
  with 
  the 
  outer 
  margin, 
  coronal 
  enamel 
  forming 
  

   a 
  narrow 
  creiiulated 
  fold 
  above 
  the 
  nearly 
  v« 
  rticabchannded 
  bt 
  

   posterior 
  border 
  similarly 
  curved, 
  but 
  of 
  greater 
  agreeing 
  in 
  

  

  other 
  respects 
  with 
  the 
  opposite 
  side; 
  inner 
  margin 
  broadly 
  rounded 
  

   or 
  obtusely 
  angular, 
  coronal 
  portion 
  well-defined 
  from 
  the 
  d< 
  

  

  somewhat 
  produced 
  and 
  shallow-channeled 
  base 
  (in 
  DlOSl 
  Bpecimenfl 
  

  

  the 
  basal 
  portion 
  is 
  worn 
  away, 
  the 
  oxowd 
  projecting 
  beyond 
  

   original 
  Bupport). 
  Coronal 
  surface 
  moderately 
  arched 
  in 
  both 
  do 
  

   tions, 
  traversed 
  a 
  little 
  posterior 
  of 
  the 
  middle 
  by 
  the 
  median 
  rid 
  

   which 
  forma 
  a 
  rather 
  prominent 
  angulation 
  partaking 
  of 
  the 
  curva- 
  

   ture 
  of 
  the 
  defining 
  1m.p1.ts. 
  anterior 
  slope 
  broader 
  than 
  the 
  some- 
  

   whal 
  more 
  concave 
  and 
  abrupt 
  posterior 
  declivity, 
  which 
  ! 
  . 
  ■■ 
  

   produced 
  into 
  as 
  obtuse 
  alation 
  at 
  the 
  extreme 
  posterior 
  angle, 
  

   u,l 
  which 
  extends 
  the 
  I 
  minating 
  in 
  an 
  obtuse 
  ipur. 
  Bur- 
  

  

  