﻿VERTEBRATES. 
  125 
  

  

  The 
  foregoing 
  diagnosis 
  of 
  the 
  characteristics 
  pertaining 
  to 
  each 
  

   of 
  the 
  several 
  dental 
  elements 
  here 
  recognized 
  as 
  having 
  formed 
  

   part 
  of 
  the 
  dentition 
  of 
  this 
  interesting 
  species, 
  presents 
  in 
  suffi- 
  

   cient 
  detail 
  the 
  peculiarities 
  which 
  distinguish 
  it 
  in 
  comparison 
  

   with 
  other 
  species 
  of 
  the 
  genus. 
  It 
  remains 
  briefly 
  to 
  observe 
  the 
  

   association 
  of 
  certain 
  teeth 
  in 
  their 
  original 
  relative 
  position 
  upon 
  

   the 
  jaws, 
  examples 
  of 
  which, 
  fortunately, 
  have 
  been 
  obtained 
  by 
  Mr. 
  

   Van 
  Home 
  and 
  Prof. 
  Worthen. 
  The 
  most 
  complete 
  specimen 
  of 
  

   the 
  mandible 
  shows 
  the 
  posterior 
  and 
  median 
  teeth 
  planted 
  upon 
  a 
  

   thin 
  semi-osseous 
  tissue 
  composed 
  of 
  coarse 
  granules 
  of 
  ossific 
  mat- 
  

   ter, 
  the 
  walls 
  of 
  which 
  are 
  strengthened 
  from 
  within 
  by 
  a 
  system 
  

   of 
  transverse 
  bars, 
  like 
  girders, 
  which 
  serve 
  to 
  maintain 
  the 
  shape 
  

   of 
  the 
  surface 
  upon 
  which 
  the 
  crushing 
  plates 
  rest. 
  The 
  teeth 
  are 
  

   separated 
  from 
  the 
  supporting 
  rami 
  by 
  a 
  film 
  of 
  calcite, 
  which 
  

   probably 
  represents 
  the 
  bulk 
  of 
  the 
  tegumentary 
  or 
  formative 
  tissue 
  

   that 
  enveloped 
  the 
  dentigerous 
  portions 
  of 
  the 
  jaw. 
  The 
  mandible 
  

   extends 
  anteriorly 
  into 
  a 
  slightly 
  produced, 
  bluntly 
  rounded 
  extrem- 
  

   ity, 
  which 
  from 
  the 
  inferior 
  surface 
  shows 
  on 
  either 
  side 
  of 
  the 
  

   symphysial 
  line 
  a 
  shallow 
  pit, 
  which 
  may 
  indicate 
  the 
  position 
  of 
  

   the 
  corresponding 
  concavity 
  of 
  the 
  dental 
  plate 
  or 
  tooth 
  occupying 
  

   the 
  extremity 
  of 
  the 
  jaw; 
  but 
  not 
  a 
  vestige 
  of 
  the 
  latter 
  exist 
  in 
  

   the 
  specimen, 
  and 
  therefore 
  in 
  regard 
  to 
  their 
  form 
  we 
  are 
  as 
  much 
  

   in 
  the 
  dark 
  as 
  heretofore. 
  Although 
  the 
  maxillary 
  anterior 
  teeth 
  

   have 
  been 
  provisionally 
  identified, 
  we 
  are 
  unable 
  to 
  conjecture 
  even 
  

   the 
  form 
  of 
  the 
  opposed 
  mandibular 
  teeth 
  — 
  whether 
  they 
  presented 
  

   a 
  series 
  of 
  distinct 
  coronal 
  crests 
  or 
  merely 
  a 
  simple 
  inrolled 
  plate. 
  

   A 
  remarkable 
  specimen 
  of 
  the 
  mandible, 
  belonging 
  to 
  the 
  Wood- 
  

   wardian 
  Museum, 
  obtained 
  from 
  the 
  mountain 
  limestone 
  of 
  Bristol, 
  

   England, 
  and 
  which 
  was 
  described 
  by 
  Professor 
  Owen, 
  (Geol. 
  Mag. 
  

   1867, 
  IV, 
  p. 
  59, 
  PI. 
  Ill, 
  f. 
  1, 
  2,) 
  shows 
  the 
  extremity 
  of 
  the 
  rami 
  of 
  

   Cochliodus 
  contortus, 
  Agass., 
  occupied 
  by 
  a 
  third 
  tooth, 
  the 
  smallest 
  

   of 
  the 
  series, 
  and 
  presenting 
  a 
  triangular 
  shaped, 
  inrolled 
  plate, 
  

   traversed 
  by 
  a 
  prominent 
  median 
  ridge 
  which 
  is 
  described 
  as 
  being 
  

   "very 
  convex 
  and 
  obliquely 
  and 
  gently 
  contorted 
  from 
  behind 
  and 
  

   below, 
  upward, 
  inward 
  and 
  forward, 
  with 
  a 
  slight 
  increase 
  of 
  breadth 
  

   or 
  fore 
  and 
  aft 
  diameter. 
  * 
  * 
  * 
  The 
  anterior 
  lobe 
  seems 
  to 
  have 
  

   had 
  the 
  form 
  of 
  a 
  small 
  tubercle, 
  but 
  its 
  summit 
  is 
  broken 
  off 
  ; 
  the 
  

   posterior 
  lobe 
  is 
  a 
  narrow, 
  seam-like, 
  raised 
  border, 
  extending 
  fur- 
  

   ther 
  back 
  on 
  the 
  outer 
  side, 
  fig. 
  2 
  a, 
  than 
  on 
  the 
  inner 
  side 
  of 
  the 
  

   ramus." 
  Our 
  specimens, 
  unfortunately, 
  afford 
  no 
  means 
  of 
  confirm- 
  

   ing 
  the 
  observations 
  based 
  on 
  the 
  Bristol 
  specimen, 
  nor 
  do 
  the 
  col- 
  

  

  