﻿VEBTEBBATES. 
  191 
  

  

  Mandibular 
  median 
  or 
  second 
  teeth 
  characterized 
  by 
  their 
  trian- 
  

   gular 
  outline, 
  rather 
  strong 
  inrollment 
  of 
  the 
  outer 
  extremity, 
  

   straight 
  postero-lateral 
  border 
  which 
  is 
  similarly 
  enameled 
  to 
  the 
  

   antero-lateral 
  border 
  of 
  last 
  above 
  described 
  posterior 
  dental 
  plates, 
  

   antero-lateral 
  border 
  rapidly 
  and 
  irregularly 
  converging 
  from 
  the 
  

   subacute 
  angle 
  of 
  the 
  broad, 
  slightly 
  arched 
  inner 
  margin. 
  Coronal 
  

   surface 
  forming 
  a 
  broad, 
  low 
  arch, 
  or 
  nearly 
  plane 
  transversely. 
  

  

  Although 
  in 
  every 
  case 
  detached 
  and 
  separated 
  from 
  their 
  natural 
  

   position 
  upon 
  the 
  jaws, 
  there 
  is 
  strong 
  inferential 
  evidence 
  of 
  the 
  

   dental 
  elements 
  described 
  above 
  having 
  constituted 
  parts 
  of 
  the 
  den- 
  

   tition 
  of 
  one 
  and 
  the 
  same 
  fish, 
  as 
  will 
  appear 
  more 
  at 
  length 
  

   under 
  the 
  head 
  of 
  specific 
  descriptions. 
  The 
  genus 
  as 
  here 
  consti- 
  

   tuted 
  does 
  some 
  violence 
  to 
  the 
  interpretation 
  of 
  the 
  affinities 
  of 
  

   the 
  teeth 
  attributed 
  by 
  authors 
  to 
  other 
  genera, 
  but 
  the 
  facts 
  are 
  

   believed 
  to 
  justify 
  no 
  other 
  conclusion, 
  while 
  in 
  the 
  typical 
  species, 
  

   at 
  least, 
  there 
  can 
  hardly 
  exist 
  a 
  doubt 
  as 
  to 
  the 
  specific 
  identity 
  of 
  

   the 
  widely 
  dissimilarly 
  shaped 
  teeth 
  alluded 
  to 
  in 
  the 
  foregoing 
  

   generic 
  diagnosis. 
  

  

  The 
  genus 
  as 
  now 
  understood 
  includes, 
  besides 
  the 
  American 
  

   forms 
  hereinafter 
  described, 
  possibly 
  a 
  form 
  of 
  teeth 
  from 
  the 
  Car- 
  

   boniferous 
  limestone 
  of 
  Bristol 
  (England), 
  vdiich 
  has 
  been 
  referred 
  

   to 
  Tomodus, 
  Agass. 
  All 
  the 
  specimens 
  of 
  maxillary 
  teeth 
  are 
  muti- 
  

   lated 
  by 
  having 
  their 
  exceedingly 
  thin 
  anterior 
  portion 
  broken 
  away 
  ; 
  

   and 
  this 
  fact 
  naturally 
  suggests 
  the 
  possible 
  occurrence 
  of 
  corres- 
  

   ponding^ 
  dental 
  plates 
  in 
  European 
  collections 
  — 
  however, 
  in 
  so 
  frag- 
  

   mentary 
  a 
  state 
  as 
  not 
  to 
  have 
  attracted 
  attention 
  to 
  their 
  probable 
  

   relationship 
  with 
  the 
  more 
  robust 
  mandibular 
  teeth. 
  

  

  Compared 
  with 
  Sandalodus, 
  N. 
  and 
  W., 
  the 
  following 
  distinguishing 
  

   features 
  are 
  especially 
  noticeable 
  : 
  The 
  posterior 
  form 
  of 
  the 
  man- 
  

   dible 
  is 
  abruptly 
  broken 
  down 
  in 
  a 
  prominent 
  mural 
  face 
  along 
  the 
  

   antero-lateral 
  border, 
  which 
  is 
  enveloped 
  in 
  a 
  widish 
  belt 
  of 
  the 
  

   coronal 
  enamel, 
  and 
  the 
  anterior 
  position 
  of 
  the 
  transversely, 
  nearly 
  

   plane, 
  well-defined 
  coronal 
  prominence, 
  in 
  all 
  which 
  there 
  is 
  striking 
  

   contrast 
  with 
  the 
  very 
  restricted 
  antero-lateral 
  articular 
  border 
  of 
  

   typical 
  homologues 
  of 
  Sandalodus. 
  In 
  the 
  posterior 
  teeth 
  of 
  the 
  

   upper 
  jaw, 
  the 
  coronal 
  prominence, 
  instead 
  of 
  being 
  situated 
  for- 
  

   ward 
  of 
  the 
  median 
  line, 
  as 
  in 
  Sandalodus, 
  rises 
  close 
  along 
  the 
  

   postero-lateral 
  border, 
  the 
  wide 
  coronal 
  declivity 
  being 
  transferred 
  

   to 
  the 
  opposite 
  side 
  of 
  the 
  tooth. 
  The 
  median 
  teeth 
  of 
  the 
  man- 
  

   dible, 
  representatives 
  of 
  which 
  belonging 
  to 
  either 
  generic 
  group 
  

   are 
  exceedingly 
  rare, 
  present 
  essentially 
  the 
  same 
  characteristics 
  

  

  