﻿VEETEBEATES. 
  171 
  

  

  therefore, 
  it 
  is 
  evident 
  the 
  form 
  held 
  a 
  median, 
  possibly 
  an 
  anterior, 
  

   position 
  probably 
  on 
  the 
  mandible. 
  It 
  remains 
  to 
  ascertain 
  its 
  

   probable 
  associate 
  forms, 
  and 
  here 
  again 
  we 
  are 
  met 
  by 
  the 
  insuf- 
  

   ficiency 
  of 
  .our 
  understanding, 
  which 
  hardly 
  more 
  than 
  suffices 
  

   vague 
  suggestion. 
  All 
  the 
  individuals 
  alike 
  of 
  all 
  the 
  varieties 
  ex- 
  

   hibit 
  a 
  peculiar 
  broad 
  undulate 
  uneven 
  course 
  in 
  the 
  borders 
  of 
  the 
  

   teeth, 
  which 
  toward 
  the 
  outer 
  inrolled 
  margin 
  usually 
  takes 
  the 
  form 
  

   of 
  a 
  more 
  or 
  less 
  distinct 
  sudden 
  constriction 
  or 
  narrowing 
  of 
  the 
  

   coronal 
  region. 
  A 
  very 
  similar 
  character 
  is 
  noticeable 
  in 
  the 
  form 
  

   previously 
  described 
  by 
  Messrs. 
  Newberry 
  and 
  Worthen 
  under 
  the 
  

   name 
  Cochliodus 
  costatus, 
  "second 
  tooth," 
  in 
  which 
  the 
  lateral 
  bor- 
  

   ders 
  are 
  similarly 
  widely 
  undulate 
  and 
  narrowed 
  towards 
  the 
  outer 
  

   margin, 
  where 
  the 
  strongly 
  inrolled 
  extremity 
  has 
  lost 
  its 
  coronal 
  

   enamel 
  presenting 
  the 
  appearance 
  of 
  having 
  been 
  embedded 
  in 
  the 
  

   integument 
  of 
  the 
  jaw, 
  precisely 
  as 
  observed 
  in 
  the 
  form 
  here 
  par- 
  

   ticularly 
  noticed. 
  Further, 
  there 
  is 
  a 
  somewhat 
  striking 
  resemblance 
  

   between 
  the 
  latter 
  forms 
  in 
  respect 
  to 
  the 
  peculiar 
  character 
  of 
  the 
  

   punctation 
  and 
  the 
  rugged 
  surface 
  of 
  the 
  crown, 
  and 
  the 
  relative 
  

   great 
  depth 
  of 
  the 
  lateral 
  border, 
  although 
  in 
  the 
  present 
  form, 
  

   apparently, 
  the 
  depth 
  of 
  the 
  borders 
  is 
  even 
  proportionately 
  greater 
  

   than 
  is 
  the 
  case 
  in 
  "C. 
  costatus" 
  ("second 
  tooth). 
  Beyond 
  this 
  we 
  

   have 
  not 
  the 
  materials 
  for 
  a 
  more 
  satisfactory 
  comparison, 
  but 
  it 
  

   seems 
  to 
  us 
  not 
  improbable 
  the 
  latter 
  forms 
  originally 
  formed 
  parts 
  

   of 
  the 
  dentition 
  of 
  one 
  and 
  the 
  same 
  species. 
  

  

  Geological 
  position 
  and 
  localities 
  : 
  Upper 
  Burlington 
  limestone 
  ; 
  

   Burlington, 
  Augusta, 
  Buffington 
  creek, 
  Louisa 
  Co., 
  Iowa; 
  Keokuk 
  

   limestone 
  ; 
  Warsaw, 
  111. 
  

  

  Genus 
  TOMODUS, 
  Agassiz. 
  

  

  Psammodtjs, 
  Agassiz, 
  1838, 
  Poissons 
  Fossils 
  III. 
  ; 
  Tomodus, 
  Agassiz, 
  

  

  Mss. 
  ; 
  1859, 
  etc. 
  

  

  The 
  genus 
  Tomodus, 
  Agassiz, 
  founded 
  upon 
  the 
  species 
  T. 
  con- 
  

   vexus 
  of 
  the 
  British 
  Mountain 
  limestone, 
  is 
  known 
  to 
  us 
  by 
  one 
  or 
  

   two 
  imperfect 
  examples 
  of 
  the 
  large 
  strongly 
  arched 
  form 
  contained 
  

   in 
  the 
  collections 
  of 
  the 
  Museum 
  of 
  Comparative 
  Zoology, 
  Cam- 
  

   bridge, 
  which, 
  however, 
  do 
  not 
  afford 
  so 
  satisfactory 
  means 
  of 
  com- 
  

   parison 
  as 
  might 
  be 
  desired 
  in 
  the 
  definition 
  of 
  their 
  generic 
  char- 
  

   acteristics. 
  We 
  are, 
  however, 
  indebted 
  to 
  the 
  courtesy 
  of 
  Lord 
  

  

  