﻿VEBTEBBATES. 
  143 
  

  

  generic 
  identity 
  of 
  the 
  forms 
  here 
  referred 
  to 
  the 
  posterior 
  position 
  

   upon 
  the 
  upper 
  and 
  lower 
  jaws 
  respectively, 
  to 
  which 
  he 
  then 
  gave 
  

   the 
  name 
  Deltodus, 
  which 
  was 
  accepted 
  by 
  European 
  authorities 
  

   and 
  recognized 
  in 
  various 
  publications. 
  Prior 
  to 
  the 
  above 
  date, 
  

   Professor 
  Frederick 
  McCoy, 
  in 
  the 
  British 
  Palaeozoic 
  Fossils, 
  1855, 
  

   recognized 
  the 
  probable 
  identity 
  of 
  the 
  narrow 
  median 
  teeth, 
  here 
  

   referred 
  to 
  the 
  mandibles, 
  with 
  the 
  so-called 
  "anterior 
  teeth" 
  of 
  

   Deltodus 
  sublcevis, 
  which 
  he 
  described 
  under 
  the 
  name 
  Poecilodus 
  

   parallelus. 
  The 
  latter 
  form 
  presents 
  the 
  same 
  general 
  figure 
  and 
  

   coronal 
  contour 
  here 
  ascribed 
  to 
  the 
  median 
  form, 
  although 
  at 
  the 
  

   same 
  time 
  it 
  presents 
  marked 
  specific 
  characters. 
  Heretofore 
  

   authors 
  have 
  not 
  essayed 
  the 
  distinct 
  definition 
  of 
  the 
  dental 
  ele- 
  

   ments 
  pertaining 
  to 
  the 
  upper 
  and 
  lower 
  jaws 
  of 
  this 
  genus, 
  and 
  in 
  

   the 
  attempt 
  in 
  that 
  direction 
  here 
  initiated 
  we 
  are 
  profoundly 
  

   conscious 
  of 
  the 
  meagre, 
  imperfect 
  data 
  from 
  which 
  to 
  draw 
  evidence 
  

   which 
  shall 
  not 
  be 
  open 
  to 
  objection 
  on 
  account 
  of 
  its 
  inconclusive 
  

   nature. 
  However 
  the 
  facts 
  are 
  briefly 
  stated, 
  and 
  if 
  they 
  do 
  not 
  

   carry 
  conviction 
  as 
  to 
  the 
  justness 
  of 
  the 
  interpretations 
  arrived 
  at 
  

   they 
  will 
  at 
  least 
  show 
  the 
  difficulties 
  in 
  the 
  way 
  of 
  the 
  student 
  

   who 
  shall 
  attempt 
  the 
  restoration 
  of 
  extinct 
  forms 
  from 
  few 
  and 
  

   detached 
  remains 
  such 
  as 
  are 
  represented 
  by 
  these 
  teetb. 
  

  

  We 
  are 
  thoroughly 
  satisfied 
  with 
  the 
  conjecture 
  of 
  Professor 
  

   McCoy 
  as 
  to 
  the 
  relative 
  position 
  and 
  specific 
  identity 
  of 
  the 
  narrow 
  

   median 
  tooth, 
  as 
  above 
  pointed 
  out 
  ; 
  but, 
  on 
  the 
  other 
  hand, 
  the 
  

   data 
  do 
  not 
  sustain 
  former 
  inferences 
  as 
  to 
  the 
  position 
  occupied 
  

   by 
  the 
  form 
  with 
  which 
  the 
  narrow 
  teeth 
  were 
  associated 
  upon 
  the 
  

   jaw. 
  The 
  so-called 
  "anterior" 
  tooth 
  possesses 
  essentially 
  the 
  char- 
  

   acteristics 
  of 
  the 
  form 
  which, 
  in 
  Cochliodus, 
  is 
  known 
  to 
  hold 
  a 
  

   posterior 
  or 
  terminal 
  position 
  upon 
  the 
  mandible. 
  The 
  latter 
  form 
  

   thus 
  transposed 
  readily 
  lends 
  itself 
  to 
  interpreting 
  the 
  median 
  posi- 
  

   tion 
  of 
  the 
  succeeding 
  narrow 
  tooth, 
  the 
  articular 
  walls 
  exactly 
  con- 
  

   forming 
  in 
  coadaptation, 
  and 
  thus 
  placed 
  they 
  assume 
  a 
  symmetrical 
  

   disposition 
  perfectly 
  in 
  consonance 
  with 
  that 
  characterizing 
  the 
  man- 
  

   dibles 
  of 
  Cochliodus, 
  Pcecilodus 
  and 
  Cestracion; 
  on 
  the 
  other 
  hand, 
  it 
  

   is 
  impossible 
  to 
  conceive 
  of 
  so 
  intimate 
  relations 
  in 
  the 
  case 
  of 
  the 
  

   so-called 
  "terminal" 
  tooth 
  with 
  either 
  of 
  the 
  forms 
  just 
  alluded 
  to. 
  

   However, 
  certain 
  features 
  are 
  noticeable 
  by 
  which 
  a 
  certain 
  striking 
  

   resemblance 
  is 
  manifest 
  between 
  the 
  median 
  form 
  and 
  that 
  here 
  

   referred 
  to 
  the 
  posterior 
  or 
  terminal 
  position 
  on 
  the 
  upper 
  jaw 
  (the 
  

   "terminal" 
  tooth 
  of 
  authors). 
  This 
  consists 
  in 
  the 
  remarkably 
  close 
  

   similarity 
  in 
  coronal 
  contour 
  which 
  obtains 
  in 
  either 
  form 
  alike, 
  

  

  