﻿VEETBBEATES. 
  213 
  

  

  Psammodus 
  plenus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XVI. 
  Pig. 
  1-4. 
  PI. 
  XVII. 
  Pig. 
  1-4. 
  

  

  Teeth 
  attain 
  large 
  size. 
  Form 
  supposed 
  to 
  pertain 
  to 
  the 
  upper 
  

   jaw 
  subrhomboidal, 
  or 
  of 
  a 
  laterally 
  elongate-trapezoidal 
  outline, 
  

   gently 
  arched 
  antro-posteriorly. 
  Margins 
  nearly 
  parallel, 
  somewhat 
  

   irregularly 
  undulated, 
  making 
  a 
  shallow 
  concavity 
  and 
  then 
  very 
  

   slightly 
  arched 
  toward 
  the 
  antero-lateral 
  angle, 
  the 
  reverse 
  occurring 
  

   in 
  the 
  posterior 
  margin 
  where 
  the 
  concavity 
  is 
  in 
  the 
  approach 
  to 
  

   the 
  postero-lateral 
  angle, 
  both 
  margins 
  inbeveled 
  or 
  perpendicular 
  

   to 
  the 
  crown 
  surface, 
  the 
  anterior 
  having 
  greatest 
  apparent 
  obliquity, 
  

   and 
  defined 
  above 
  by 
  the 
  narrow 
  coronal 
  belt 
  which 
  constitutes 
  less 
  

   than 
  one-fourth 
  the 
  depth 
  of 
  the 
  face 
  ; 
  the 
  inner 
  border 
  is 
  nearly 
  

   straight, 
  showing 
  a 
  faint 
  angulation 
  a 
  little 
  posterior 
  of 
  the 
  middle, 
  

   and 
  a 
  narrower 
  truncated 
  articular 
  facet 
  at 
  the 
  posterior 
  angle, 
  the 
  

   coronal 
  folds 
  of 
  the 
  margins 
  forming 
  a 
  continuous 
  belt 
  well 
  defined 
  

   from 
  the 
  moderately 
  channeled 
  basal 
  portion, 
  which 
  terminates 
  in- 
  

   feriorly 
  in 
  a 
  narrow 
  rim 
  ; 
  the 
  outer 
  border 
  is 
  very 
  gently 
  arched, 
  

   converging 
  at 
  an 
  angle 
  of 
  about 
  15°, 
  more 
  or 
  less, 
  with 
  the 
  oppo- 
  

   site 
  border, 
  and 
  generally 
  sharply 
  rounded 
  at 
  the 
  anterior 
  angle, 
  

   terminating 
  in 
  a 
  more 
  or 
  less 
  produced, 
  acute 
  angle 
  posteriorly; 
  in 
  

   small 
  or 
  earlier-formed 
  teeth 
  the 
  outer 
  border 
  is 
  sharply 
  inbeveled 
  

   above 
  and 
  somewhat 
  deeply 
  channeled, 
  limited 
  by 
  the 
  narrow 
  flange 
  

   or 
  basal 
  rim 
  below; 
  but 
  in 
  larger 
  individuals 
  the 
  basal 
  portion 
  in- 
  

   creases 
  in 
  prominence, 
  forming 
  a 
  massive 
  border 
  extending 
  consid- 
  

   erably 
  beyond 
  the 
  coronal 
  limits 
  and 
  terminating 
  in 
  a 
  more 
  or 
  less 
  

   produced 
  spur 
  at 
  the 
  posterior 
  angle. 
  Coronal 
  surface 
  smooth, 
  

   gently 
  arched 
  longitudinally 
  and 
  between 
  the 
  lateral 
  borders, 
  making 
  a 
  

   broad, 
  shallow 
  concavity, 
  forming 
  an 
  angle 
  along 
  the 
  inner 
  border 
  

   and 
  sharply 
  rounded 
  in 
  the 
  narrow 
  coronal 
  fold 
  along 
  the 
  outer 
  

   border, 
  where 
  it 
  is 
  well 
  defined 
  from 
  the 
  basal 
  portion 
  in 
  small 
  and 
  

   large 
  examples 
  alike. 
  The 
  crown 
  surface 
  is 
  uniformly 
  minutely 
  

   punctate, 
  the 
  pores 
  being 
  considerably 
  spaced 
  and 
  confined 
  within 
  

   the 
  easily 
  discerned 
  vertical 
  prisms. 
  However, 
  the 
  surface 
  structure 
  

   varies 
  according 
  to 
  the 
  state 
  of 
  preservation. 
  In 
  much 
  worn 
  exam- 
  

   ples 
  the 
  punctse 
  are 
  coarse 
  and 
  crowded, 
  while 
  in 
  others 
  under 
  an 
  

   ordinary 
  lens 
  the 
  radi 
  of 
  calcigerous 
  tubes 
  around 
  the 
  orifices 
  of 
  

   the 
  pores 
  and 
  the 
  minute 
  prismatic 
  structure 
  of 
  the 
  inter-spaces 
  are 
  

   beautifully 
  revealed. 
  Again, 
  the 
  lines 
  of 
  growth 
  generally 
  describe 
  

   a 
  segment 
  of 
  a 
  broad 
  circle 
  with 
  the 
  convexity 
  toward 
  the 
  posterior 
  

  

  