﻿428 
  L. 
  C 
  MIALL 
  ON 
  THE 
  REMAINS 
  OF 
  1ABYIUNTHODONTA 
  

  

  The 
  upper 
  surface 
  of 
  the 
  fragment 
  shows 
  the 
  two 
  longitudinal 
  

   ridges 
  of 
  the 
  articular 
  bone. 
  Of 
  these, 
  the 
  internal 
  still 
  remains 
  for 
  

   3§ 
  in. 
  : 
  its 
  upper 
  border 
  is 
  thick 
  and 
  rounded 
  in 
  front, 
  where 
  it 
  

   overhangs 
  the 
  internal 
  mandibular 
  foramen 
  ; 
  but 
  behind 
  it 
  is 
  bevelled 
  

   off 
  to 
  an 
  edge 
  upon 
  its 
  inner 
  side. 
  The 
  fragment 
  of 
  the 
  external 
  

   ridge 
  is 
  only 
  1§ 
  in. 
  in 
  length, 
  corresponding 
  in 
  position 
  to 
  the 
  ante- 
  

   rior 
  half 
  of 
  the 
  inner 
  ridge. 
  Its 
  upper 
  surface 
  exhibits 
  irregular 
  

   longitudinal 
  ridges 
  and 
  striations. 
  The 
  two 
  ridges 
  converge 
  in 
  

   front, 
  nearly 
  touching 
  "where 
  they 
  are 
  broken 
  off; 
  but 
  behind 
  they 
  

   are 
  separated 
  by 
  a 
  distance 
  of 
  about 
  | 
  in. 
  The 
  anterior 
  broken 
  end 
  

   of 
  the 
  fragment 
  shows 
  that 
  the 
  section 
  of 
  the 
  alveolar 
  canal, 
  at 
  

   about 
  the 
  level 
  of 
  the 
  foramen, 
  is 
  nearly 
  elliptical, 
  the 
  external 
  

   plate 
  being 
  strongly 
  curved 
  inwards 
  in 
  its 
  upper 
  half. 
  In 
  both, 
  the 
  

   foregoing 
  examples 
  of 
  Diadetognathus, 
  as 
  also 
  in 
  the 
  mandible 
  of 
  

   Mastodonsaurus 
  pachygnathus, 
  an 
  aperture 
  exists 
  upon 
  the 
  upper 
  

   surface 
  of 
  the 
  ramus, 
  between 
  the 
  two 
  parallel 
  and 
  vertical 
  plates 
  

   of 
  the 
  articular 
  bone. 
  The 
  upper 
  edges 
  of 
  these 
  plates 
  bear 
  

   traces 
  of 
  union 
  with 
  overlying 
  bone 
  or 
  cartilage 
  ; 
  but 
  no 
  element 
  of 
  

   the 
  mandible 
  can 
  be 
  proved 
  to 
  have 
  completed 
  the 
  gap. 
  It 
  is 
  pos- 
  

   sible 
  that 
  a 
  slip 
  from 
  the 
  dentary, 
  internal 
  to 
  that 
  which 
  is 
  pre- 
  

   served 
  in 
  the 
  fossil 
  No. 
  7, 
  and 
  diverging 
  from 
  it, 
  may 
  have 
  overlain 
  

   the 
  articular 
  bone 
  as 
  far 
  back 
  as 
  the 
  condyle 
  ; 
  but 
  there 
  is 
  no 
  evi- 
  

   dence 
  that 
  such 
  was 
  the 
  case. 
  

  

  This 
  fragment 
  entirely 
  agrees 
  with 
  No. 
  7, 
  and 
  must 
  be 
  referred 
  

   to 
  the 
  same 
  species. 
  

  

  10. 
  Diadetognathus 
  varvicensis 
  — 
  fragment 
  of 
  left 
  ramus 
  of 
  man- 
  

   dible. 
  Coton 
  End, 
  1872. 
  

  

  The 
  chief 
  interest 
  of 
  this 
  fossil 
  lies 
  in 
  the 
  row 
  of 
  mandibular 
  

   teeth. 
  Eighteen 
  of 
  these 
  are 
  more 
  or 
  less 
  perfectly 
  preserved 
  ; 
  and 
  

   there 
  are 
  spaces 
  for 
  eight 
  more. 
  As 
  in 
  the 
  previous 
  fragment, 
  the 
  

   teeth 
  are 
  much 
  compressed 
  in 
  an 
  antero 
  -posterior 
  direction. 
  They 
  

   are 
  lodged 
  in 
  an 
  alveolus 
  of 
  the 
  dentary 
  bone. 
  As 
  usual 
  in 
  La- 
  

   byrinthodonts, 
  the 
  outer 
  wall 
  of 
  the 
  alveolus 
  rises 
  higher 
  than 
  the 
  

   inner, 
  the 
  difference 
  in 
  height 
  amounting 
  in 
  the 
  present 
  case 
  to 
  | 
  in. 
  

   The 
  teeth 
  are 
  firmly 
  attached 
  both 
  to 
  the 
  floor 
  and 
  the 
  sides 
  of 
  the 
  

   alveolus, 
  so 
  that, 
  where 
  they 
  have 
  fallen 
  out, 
  ridges 
  corresponding 
  

   to 
  the 
  spaces 
  between 
  the 
  dentinal 
  folds 
  project 
  from 
  the 
  whole 
  

   width 
  of 
  the 
  alveolar 
  groove 
  (outer 
  wall, 
  floor, 
  and 
  inner 
  wall). 
  

   The 
  base 
  of 
  the 
  tooth 
  is 
  a 
  parallelopiped, 
  whose 
  transverse 
  width 
  is 
  

   about 
  twice 
  the 
  longitudinal 
  measurement. 
  From 
  the 
  level 
  of 
  the 
  

   inner 
  alveolar 
  parapet, 
  upwards, 
  the 
  tooth 
  tapers 
  and 
  grows 
  more 
  

   and 
  more 
  conical. 
  Its 
  sides 
  are 
  ornamented 
  with 
  vertical 
  striae, 
  

   easily 
  visible 
  to 
  the 
  naked 
  eye. 
  The 
  largest 
  tooth 
  yet 
  standing 
  is 
  

   | 
  in. 
  high. 
  It 
  may 
  have 
  lost 
  about 
  1 
  of 
  its 
  original 
  height 
  ; 
  and 
  as 
  

   the 
  bases 
  of 
  some 
  other 
  teeth 
  are 
  much 
  larger 
  than 
  that 
  of 
  the 
  one 
  

   selected 
  for 
  measurement, 
  it 
  appears 
  that 
  an 
  unbroken 
  tooth 
  may 
  

   easily 
  have 
  attained 
  an 
  inch 
  in 
  height. 
  A 
  detached 
  fragment, 
  im- 
  

   bedded 
  in 
  tbe 
  matrix 
  between 
  two 
  standing 
  teeth, 
  shows 
  the 
  true 
  

   crown. 
  This 
  is 
  sharply 
  two-edged, 
  and 
  much 
  longer 
  and 
  more 
  

   slender 
  than 
  usual. 
  It 
  is 
  to 
  be 
  hoped 
  that 
  the 
  authorities 
  of 
  the 
  

  

  