﻿VEBTEBBATES. 
  187 
  

  

  Only 
  three 
  examples 
  of 
  the 
  aboved 
  escribed 
  form 
  occur 
  in 
  the 
  collec- 
  cl 
  

   tions, 
  and 
  of 
  these 
  only 
  one 
  displays 
  the 
  entire 
  outline 
  and 
  general 
  

   coronal 
  contour. 
  The 
  latter 
  example 
  was 
  discovered 
  by 
  Mr. 
  L. 
  A. 
  

   Cox, 
  in 
  the 
  rock 
  excavations 
  for 
  the 
  government 
  canal 
  around 
  the 
  

   Keokuk 
  rapids 
  on 
  the 
  Mississippi, 
  and 
  to 
  whom 
  we 
  also 
  owe 
  the 
  

   opportunity 
  to 
  examine 
  additional 
  material 
  illustrating 
  the 
  dentition 
  

   of 
  this 
  extraordinary 
  species. 
  We 
  have 
  little 
  doubt 
  as 
  to 
  the 
  

   specific 
  relations 
  of 
  the 
  above 
  described 
  form, 
  and 
  from 
  its 
  peculiar 
  

   outline 
  and 
  coronal 
  contour, 
  and 
  the 
  strong 
  spirally 
  inrolled 
  ex- 
  

   tremity 
  (which 
  makes 
  a 
  complete 
  revolution, 
  then 
  becomes 
  involved 
  

   in 
  the 
  vaso-dentine, 
  forming 
  a 
  solid 
  mass 
  except 
  for 
  the 
  minutest 
  

   perforation 
  intercommunicating 
  with 
  either 
  border 
  through 
  its 
  

   center), 
  we 
  are 
  led 
  to 
  identify 
  it 
  with 
  the 
  mandibular 
  median 
  form 
  

   of 
  this 
  genus. 
  The 
  specimen 
  affording 
  the 
  above 
  measurements 
  

   doubtless 
  belonged 
  to 
  a 
  mature 
  fish; 
  the 
  middle 
  portion 
  of 
  the 
  

   crown, 
  indeed, 
  is 
  excessively 
  worn, 
  affording 
  a 
  striking 
  illustration 
  

   of 
  the 
  severe 
  usage 
  to 
  which 
  the 
  teeth 
  were 
  subjected 
  during 
  life. 
  

  

  It 
  is 
  our 
  belief 
  that 
  the 
  form 
  originally 
  described 
  under 
  the 
  name 
  

   Deltodus 
  grandis, 
  N. 
  and. 
  W., 
  is 
  specifically 
  identical 
  with 
  Sandalo- 
  

   dus 
  Icevissimus, 
  N. 
  and 
  W., 
  which 
  latter 
  name 
  was 
  applied 
  to 
  the 
  

   long 
  teeth 
  .which 
  we 
  presume 
  to 
  have 
  held 
  the 
  posterior 
  place 
  

   upon 
  the 
  upper 
  jaw, 
  the 
  fornler 
  form 
  occupying 
  the 
  opposed 
  posi- 
  

   tion 
  upon 
  the 
  mandible. 
  The 
  meagre 
  data 
  might 
  not 
  be 
  deemed 
  

   as 
  affording 
  sufficient 
  grounds 
  for 
  the 
  limitation 
  of 
  the 
  three 
  above- 
  

   mentioned 
  forms 
  ; 
  but 
  the 
  facts 
  themselves, 
  though 
  few, 
  seem 
  to 
  us 
  

   to 
  offer 
  something 
  more 
  than 
  a 
  mere 
  suggestion 
  of 
  such 
  a 
  relation- 
  

   ship. 
  The 
  names 
  Sandalodus 
  grandis, 
  N. 
  and 
  W., 
  Cochliodus 
  ? 
  cras- 
  

   sus, 
  N. 
  and 
  W., 
  Psammodus 
  semi-cylindricus, 
  N. 
  and 
  W., 
  and 
  Psam- 
  

   modus 
  ? 
  rhomboideus, 
  N. 
  and 
  W., 
  were 
  applied 
  to 
  abnormally 
  worn 
  

   and 
  otherwise 
  imperfect 
  examples 
  of 
  the 
  maxillary 
  posterior 
  form 
  

   of 
  this 
  species. 
  

  

  Geological 
  position 
  and 
  localities: 
  Keokuk 
  limestone; 
  Keokuk 
  and 
  

   Bentonsport, 
  (Iowa,) 
  Hamilton, 
  and 
  Warsaw, 
  (111.,) 
  Boonville, 
  (Mo.). 
  

  

  Sandalodus, 
  sp.? 
  

  

  PL 
  XII, 
  Pig. 
  5,6. 
  

  

  The 
  Warsaw 
  limestone 
  has 
  thus 
  far 
  afforded 
  very 
  meagre 
  and 
  

   imperfectly 
  preserved 
  material 
  referable 
  to 
  the 
  genus 
  Sandalodus. 
  

   The 
  Warsaw 
  horizon 
  at 
  the 
  mouth 
  of 
  the 
  Piasa, 
  above 
  Alton, 
  has 
  

  

  