﻿VEKTEBEATES. 
  67 
  

  

  face 
  minutely 
  and 
  closely 
  punctate. 
  The 
  proportionate 
  dimensions 
  

   of 
  large 
  examples 
  vary 
  considerably, 
  according 
  to 
  the 
  state 
  of 
  trun- 
  

   cation 
  of 
  the 
  inrolled 
  extremity; 
  in 
  other 
  respects, 
  however, 
  as 
  in 
  

   general 
  outline 
  and 
  coronal 
  contour, 
  the 
  observable 
  variation 
  of 
  in- 
  

   dividual 
  teeth 
  is 
  comparatively 
  unimportant, 
  save 
  what 
  is 
  attribu- 
  

   table 
  to 
  wear 
  while 
  in 
  use. 
  Both 
  the 
  anterior 
  and 
  posterior 
  borders 
  

   are 
  faintly 
  undulated, 
  suggesting 
  their 
  association 
  with 
  series 
  of 
  

   smaller 
  teeth. 
  The 
  latter 
  condition 
  is 
  even 
  more 
  markedly 
  exhibited 
  

   in 
  the 
  teeth 
  (including 
  this 
  particular 
  form,) 
  from 
  the 
  Chester 
  lime- 
  

   stone, 
  Psephodus 
  crenulatus, 
  N. 
  and 
  W., 
  with 
  which 
  the 
  teeth 
  de- 
  

   scribed 
  under 
  the 
  name 
  Aspidodus 
  convolutus, 
  N. 
  and 
  W., 
  is 
  specific- 
  

   ally 
  identical. 
  The 
  posterior 
  sinuations 
  are 
  fewer, 
  indicating 
  larger 
  

   teeth 
  for 
  the 
  contiguous 
  series 
  than 
  those 
  at 
  the 
  opposite 
  border. 
  

   The 
  relations 
  of 
  crown 
  to 
  base 
  are 
  shown 
  in 
  the 
  illustrations 
  given 
  

   of 
  the 
  teeth 
  in 
  question. 
  These 
  teeth 
  probably 
  occupied 
  a 
  median 
  

   position 
  upon 
  the 
  rami 
  of 
  the 
  mandible. 
  An 
  ordinary- 
  sized 
  tooth 
  

   measures 
  in 
  greatest 
  breadth 
  between 
  the 
  inner 
  angles 
  40 
  mm; 
  

   ditto, 
  across 
  outer 
  extremity 
  25 
  mm; 
  length 
  along 
  antero-lateral 
  

   border 
  20 
  m 
  m 
  ; 
  ditto, 
  postero-lateral 
  border 
  30 
  m 
  m 
  ; 
  depth 
  of 
  tooth 
  

   at 
  middle 
  of 
  anterior 
  border 
  3 
  mm; 
  ditto, 
  middle 
  of 
  inner 
  margin 
  

   5mm; 
  greatest 
  length 
  along 
  coronal 
  ridge 
  40 
  m 
  m. 
  The 
  propor- 
  

   tions 
  will, 
  of 
  course, 
  be 
  found 
  to 
  vary 
  in 
  individuals 
  of 
  the 
  same 
  

   age, 
  in 
  accordance 
  with 
  the 
  abbreviation 
  of 
  the 
  outer 
  extremity. 
  

  

  Teeth 
  strikingly 
  in 
  contrast 
  with 
  the 
  preceding 
  form, 
  occurring 
  in 
  

   the 
  collection 
  with 
  the 
  same 
  frequency, 
  but 
  possessing 
  superficial 
  

   characters 
  which 
  strongly 
  suggest 
  their 
  intimate 
  connection 
  with 
  that 
  

   form/ 
  may 
  be 
  regarded 
  as 
  the 
  opposed 
  form 
  of 
  the 
  upper 
  jaw. 
  They 
  

   are 
  distinguishable 
  by 
  their 
  trapezoidal 
  outline 
  and 
  relatively 
  uniform 
  

   low 
  coronal 
  surface, 
  and 
  proportionally 
  less 
  robust 
  build. 
  Outer 
  ex- 
  

   tremity 
  obliquely 
  truncated 
  in 
  the 
  same 
  direction 
  observed 
  in 
  the 
  

   previously 
  mentioned 
  form, 
  or 
  from 
  the 
  anterior 
  angle 
  outward 
  and 
  

   downward, 
  and 
  forming 
  nearly 
  a 
  right 
  angle 
  with 
  the 
  antero-lateral 
  

   border, 
  the 
  narrow 
  coronal 
  fold 
  projecting 
  beyond 
  the 
  furrowed 
  base, 
  

   and 
  somewhat 
  irregular 
  in 
  outline, 
  forming 
  an 
  articular 
  edge 
  with 
  a 
  

   similar 
  preceding 
  tooth 
  of 
  the 
  same 
  series 
  ; 
  antero-lateral 
  border 
  

   proportionately 
  shorter 
  than 
  in 
  the 
  first 
  noticed 
  form, 
  slightly 
  

   curved 
  sigmoidally, 
  nearly 
  vertical, 
  with 
  a 
  narrow 
  channel 
  defining 
  

   the 
  crenulated 
  coronal 
  fold 
  from 
  the 
  base, 
  and 
  more 
  or 
  less 
  dis- 
  

   tinctly 
  undulated; 
  postero-lateral 
  border 
  somewhat 
  more 
  strongly 
  

   curved, 
  obtusely 
  rounded 
  at 
  the 
  inner 
  posterior 
  angle, 
  the 
  crenulated 
  

   coronal 
  fold 
  slightly 
  overarching 
  the 
  basal 
  portion, 
  which 
  is 
  also 
  

  

  oo 
  

  

  