﻿VEBTEBBATES. 
  103 
  

  

  usually 
  show 
  marked 
  tendency 
  to 
  elongation 
  in 
  the 
  direction 
  of 
  the 
  

   inrollment 
  of 
  the 
  tooth 
  ; 
  the 
  inner 
  surface 
  shows 
  a 
  dense 
  layer 
  of 
  

   enamel 
  with 
  fine 
  lines 
  of 
  growth 
  parallel 
  with 
  the 
  inner 
  margin. 
  

   Greatest 
  transverse 
  diameter 
  of 
  the 
  tooth, 
  20 
  mm.; 
  length 
  along 
  

   antero-lateral 
  border, 
  6.5 
  m 
  m. 
  ; 
  greatest 
  longitudinal 
  diameter, 
  10.5 
  

   mm. 
  

  

  Posterior 
  tooth 
  of 
  the 
  mandible 
  sub-quadrangular 
  in 
  outline, 
  rather 
  

   strongly 
  inrolled 
  and 
  longitudinally 
  arched 
  ; 
  corresponding 
  in 
  size 
  with 
  

   the 
  previously-noticed 
  form. 
  The 
  moderate 
  and 
  regular 
  arching 
  of 
  

   the 
  inner 
  margin 
  interrupted 
  by 
  the 
  broadly-rounded 
  base 
  of 
  the 
  

   coronal 
  prominence; 
  antero-lateral 
  border 
  with 
  a 
  slight 
  oblique 
  

   course 
  outward 
  and 
  backward, 
  enamel 
  fold 
  relatively 
  deep 
  and 
  in- 
  

   beveled 
  to 
  the 
  shallow, 
  channeled 
  basal 
  rim 
  ; 
  postero-lateral 
  border 
  

   very 
  gradually 
  converging, 
  making 
  an 
  angle 
  of 
  10° 
  or 
  15° 
  with 
  the 
  

   opposite 
  side, 
  the 
  narrow 
  enamel 
  fold 
  well 
  defined 
  from 
  the 
  basal 
  

   portion, 
  which 
  forms 
  a 
  shallow 
  rim 
  projecting 
  considerably 
  beyond 
  

   the 
  limits 
  of 
  the 
  crown. 
  Median 
  prominence 
  regularly 
  and 
  broadly 
  

   arched 
  transversely, 
  culminating 
  a 
  little 
  posterior 
  of 
  the 
  median 
  

   line, 
  and 
  occupying 
  quite 
  half 
  of 
  the 
  lateral 
  diameter 
  of 
  the 
  crown; 
  

   posteriorly, 
  the 
  slope 
  merges 
  into 
  the 
  shallow 
  concavity 
  bordered 
  

   exteriorly 
  by 
  the 
  gently-upraised 
  alation, 
  in 
  front 
  defined 
  by 
  a 
  faint 
  

   angulation 
  from 
  the 
  wide, 
  slightly 
  convex 
  belt 
  intervening 
  between 
  

   the 
  median 
  lobe 
  and 
  the 
  antero-lateral 
  border. 
  The 
  surface 
  of 
  the 
  

   anterior 
  belt 
  is 
  marked 
  by 
  faint, 
  revolving 
  plicae, 
  and 
  along 
  the 
  

   inner 
  margin 
  the 
  enamel 
  coating 
  shows 
  more 
  or 
  less 
  distinct 
  parallel 
  

   undulations, 
  or 
  lines 
  of 
  growth, 
  the 
  outer 
  half 
  of 
  the 
  coronal 
  surface 
  

   exhibiting 
  the 
  usual 
  evidences 
  of 
  excessive 
  trituration, 
  the 
  entire 
  

   coronal 
  area 
  minutely 
  and 
  closely 
  punctate, 
  the 
  punctse 
  showing 
  the 
  

   longitudinal 
  elongation 
  precisely 
  after 
  the 
  manner 
  observed 
  in 
  con- 
  

   nection 
  with 
  the 
  opposed 
  maxillary 
  teeth. 
  Breadth 
  across 
  inner 
  

   margin, 
  17 
  mm. 
  ; 
  longitudinal 
  diameter 
  along 
  the 
  axis 
  of 
  median 
  

   lobe, 
  9.5 
  mm 
  ; 
  length 
  along 
  antero-lateral 
  border, 
  7 
  mm. 
  

  

  The 
  two 
  forms 
  of 
  teeth 
  described 
  above 
  are 
  represented 
  in 
  equal 
  

   numbers 
  in 
  the 
  collections, 
  and 
  their 
  uniform 
  association 
  and 
  agree- 
  

   ment 
  in 
  size 
  and 
  superficial 
  characters 
  preclude 
  any 
  doubt 
  as 
  to 
  

   their 
  specific 
  identity. 
  As 
  commonly 
  occurs 
  in 
  the 
  teeth 
  of 
  this 
  

   family, 
  in 
  consequence 
  of 
  the 
  attenuation 
  of 
  the 
  borders, 
  seldom 
  is 
  

   a 
  specimen 
  met 
  with 
  showing 
  the 
  antero-lateral 
  border 
  entire, 
  and 
  

   indeed 
  in 
  the 
  majority 
  of 
  examples 
  of 
  the 
  mandibular 
  form 
  the 
  

   posterior 
  wing 
  or 
  alation 
  is 
  also 
  mutilated 
  or 
  broken 
  away. 
  

  

  