﻿VEKTEBEATES. 
  225 
  

  

  originally 
  noticed 
  by 
  Messrs. 
  Newberry 
  and 
  Worthen. 
  The 
  original 
  

   specimen 
  is 
  probably 
  that 
  of 
  an 
  immature 
  tooth 
  which 
  had 
  not 
  

   been 
  brought 
  into 
  use 
  prior 
  to 
  the 
  destruction 
  of 
  its 
  possessor, 
  and 
  

   it 
  is 
  owing 
  to 
  this 
  fact 
  that 
  it 
  presents 
  merely 
  the 
  coronal 
  crest 
  or 
  

   shell 
  entirely 
  detached 
  from 
  the 
  base, 
  which 
  was 
  of 
  a 
  coarse 
  porous 
  

   structure 
  and 
  less 
  solidified 
  than 
  the 
  layer 
  more 
  strictly 
  pertaining 
  

   to 
  the 
  coronal 
  region 
  ; 
  also 
  to 
  the 
  same 
  state 
  of 
  things 
  is 
  doubtless 
  

   attributable 
  the 
  very 
  perfect 
  state 
  of 
  preservation 
  of 
  the 
  rugose 
  

   ornamentation, 
  which 
  in 
  this 
  instance 
  occupies 
  the 
  entire 
  coronal 
  

   surface. 
  Fragments 
  of 
  teeth 
  identical 
  in 
  contour 
  and 
  ornamentation 
  

   are 
  readily 
  identified 
  with 
  the 
  above 
  specimen; 
  but 
  otbers 
  bearing- 
  

   unmistakable 
  evidence 
  of 
  excessive 
  abrasion 
  while 
  in 
  use, 
  present 
  a 
  

   nearly 
  plane 
  coronal 
  surface 
  with 
  only 
  traces 
  of 
  the 
  rugae 
  remaining 
  

   in 
  the 
  more 
  depressed 
  portions 
  of 
  the 
  surface. 
  The 
  latter, 
  from 
  the 
  

   general 
  outline, 
  apparent 
  original 
  contour, 
  and 
  the 
  posteriorly 
  gently 
  

   convex 
  course 
  of 
  the 
  transverse 
  depressions 
  which 
  also 
  correspond 
  

   with 
  the 
  lines 
  of 
  growth, 
  strongly 
  indicate 
  their 
  identity 
  with 
  the 
  

   original 
  specimen, 
  and 
  it 
  is 
  with 
  the 
  aid 
  of 
  these 
  maturer 
  examples 
  

   that 
  the 
  outline 
  of 
  the 
  form 
  may 
  be 
  more 
  definitely 
  sketched, 
  the 
  

   type 
  specimen 
  being 
  imperfect 
  at 
  either 
  lateral 
  border. 
  

  

  The 
  type 
  example 
  is 
  probably 
  a 
  representative 
  of 
  the 
  form 
  pro- 
  

   visionally 
  identified 
  with 
  the 
  upper 
  jaw. 
  The 
  teeth 
  attain 
  medium 
  

   size, 
  quadrilateral 
  in 
  outline. 
  In 
  more 
  or 
  less 
  worn 
  specimens, 
  the 
  

   usual 
  condition 
  of 
  the 
  examples 
  that 
  have 
  been 
  found, 
  the 
  coronal 
  

   region 
  presents 
  a 
  moderate 
  longitudinal 
  convexity, 
  and 
  a 
  slight 
  

   transverse 
  concavity, 
  in 
  which 
  direction 
  the 
  surface 
  shows 
  a 
  more 
  

   or 
  less 
  distinct 
  undulation, 
  the 
  plane 
  posterior 
  slope 
  preserving 
  

   traces 
  of 
  the 
  original 
  rugose 
  ornamentation. 
  The 
  coronal 
  surface 
  

   of 
  unworn 
  teeth, 
  like 
  the 
  type 
  specimen 
  of 
  the 
  form, 
  shows 
  a 
  rather 
  

   strongly 
  arched 
  contour 
  from 
  behind 
  forward, 
  produced 
  by 
  a 
  con- 
  

   spicuous 
  transverse 
  ridge, 
  from 
  which 
  the 
  surface 
  gently 
  slopes 
  

   with 
  slight 
  concavity 
  to 
  the 
  anterior 
  margin, 
  more 
  steeply 
  sloped 
  

   behind 
  to 
  a 
  slight 
  impressed 
  angle, 
  whence 
  the 
  surface 
  presents 
  a 
  

   nearly 
  plane 
  area 
  of 
  variable 
  width, 
  terminating 
  in 
  the 
  posterior 
  

   margin, 
  and 
  irregularly 
  undulated 
  longitudinally; 
  the 
  crest 
  of 
  the 
  

   transverse 
  ridge 
  is 
  gently 
  sagged 
  throughout 
  the 
  greater 
  part 
  of 
  its 
  

   extent, 
  and 
  on 
  nearing 
  the 
  outer 
  ( 
  ?) 
  border 
  it 
  is 
  somewhat 
  steeply 
  

   sloped 
  into 
  what 
  appears 
  to 
  have 
  formed 
  a 
  shallow, 
  narrow 
  depres- 
  

   sion 
  just 
  within 
  the 
  outer 
  coronal 
  fold; 
  even 
  in 
  worn 
  examples 
  the 
  

   latter 
  conformation 
  of 
  the 
  coronal 
  surface 
  is 
  more 
  or 
  less 
  discern- 
  

   ible, 
  but 
  the 
  inner 
  border 
  is 
  angularly 
  rounded 
  to 
  the 
  nearly 
  ver- 
  

  

  —15 
  

  

  