﻿VERTEBRATES. 
  129 
  

  

  the 
  point 
  of 
  inrollment 
  and 
  the 
  sharply 
  rounded 
  posterior 
  extremity, 
  

   the 
  basal 
  portion 
  extending 
  considerably 
  beyond 
  the 
  limits 
  of 
  the 
  

   crown 
  forming 
  a 
  thin 
  marginal 
  rim 
  posteriorly 
  ; 
  inner 
  margin 
  broadly 
  

   arched 
  in 
  general 
  course, 
  suddenly 
  constricted 
  in 
  front 
  of 
  the 
  pos- 
  

   terior 
  lobe, 
  and 
  thence 
  more 
  gently 
  arched 
  to 
  the 
  anterior 
  angle. 
  

   Coronal 
  region 
  presents 
  strong 
  contour 
  contrasts, 
  posterior 
  lobe 
  

   prominent, 
  constituting 
  somewhat 
  more 
  than 
  half 
  the 
  lateral 
  diam- 
  

   eter 
  of 
  the 
  tooth, 
  abruptly 
  rising 
  in 
  front 
  into 
  the 
  rounded 
  crest 
  

   from 
  which 
  the 
  slope 
  in 
  the 
  opposite 
  direction 
  gently 
  descends 
  in 
  

   slight 
  transverse 
  convexity 
  to 
  the 
  postero-lateral 
  border, 
  where 
  the 
  

   coronal 
  enamel 
  forms 
  a 
  thick 
  inbeveled 
  fold 
  distinctly 
  defined 
  from 
  

   the 
  basal 
  portion 
  ; 
  the 
  anterior 
  neck 
  is 
  separated 
  from 
  the 
  posterior 
  

   prominence 
  by 
  a 
  deep 
  narrow 
  depression, 
  in 
  well-preserved 
  exam- 
  

   ples 
  showing 
  a 
  distinct 
  narrow 
  secondary 
  ridge 
  with 
  steep 
  declirity 
  

   bordering" 
  the 
  median 
  depression, 
  a 
  transversely 
  more 
  gently 
  convex 
  

   wider 
  belt 
  intervening 
  between 
  the 
  latter 
  and 
  the 
  shallow 
  furrow 
  

   defining 
  the 
  posterior 
  limits 
  of 
  the 
  narrow 
  relatively 
  prominent 
  belt 
  

   along 
  the 
  antero-lateral 
  border, 
  where 
  the 
  coronal 
  enamel 
  forms 
  a 
  

   well-marked 
  fold 
  inbeveled 
  to 
  the 
  basal 
  portion. 
  Superficial 
  punc- 
  

   tation 
  the 
  same 
  as 
  in 
  the 
  opposed 
  mandibular 
  teeth. 
  A 
  mature 
  

   tooth 
  measures 
  in 
  greatest 
  diameter 
  of 
  crown 
  at 
  the 
  inner 
  margin, 
  

   22.5 
  mm., 
  the 
  basal 
  portion 
  being 
  considerably 
  farther 
  prolonged 
  

   into 
  the 
  posterior 
  spur 
  ; 
  length 
  of 
  antero-lateral 
  border 
  to 
  point 
  of 
  

   inrollment, 
  8 
  mm. 
  ; 
  median 
  furrow 
  at 
  inner 
  margin, 
  13 
  mm. 
  distant 
  

   from 
  posterior 
  extremity. 
  

  

  Associated 
  with 
  the 
  above 
  described 
  forms, 
  the 
  collections 
  contain 
  

   a 
  few 
  examples 
  of 
  Helodus-like 
  teeth, 
  mostly 
  isolated 
  individuals, 
  but 
  

   occasionally 
  in 
  series, 
  which 
  we 
  are 
  inclined 
  to 
  identify 
  with 
  the 
  

   present 
  species. 
  One 
  of 
  these 
  series, 
  in 
  the 
  collection 
  of 
  Professor 
  

   Worthen, 
  presents 
  a 
  series 
  of 
  four 
  teeth 
  firmly 
  soldered 
  at 
  the 
  im- 
  

   piugement 
  of 
  their 
  bases, 
  without 
  visible 
  suture, 
  forming 
  a 
  deltoid 
  

   figure, 
  belonging 
  to 
  the 
  right 
  ramus 
  of 
  the 
  upper 
  jaw. 
  The 
  three 
  

   outer 
  teeth 
  regularly 
  and 
  gradually 
  diminish 
  in 
  size 
  from 
  behind 
  

   outward, 
  except 
  the 
  innermost 
  one, 
  which 
  presents 
  the 
  usual 
  condi- 
  

   tion 
  of 
  immature 
  coronal 
  ridge 
  apparently 
  resting 
  upon 
  the 
  inner 
  

   deep 
  basal 
  border 
  of 
  the 
  immediately 
  preceding 
  tooth. 
  The 
  anterior 
  

   basal 
  margin 
  of 
  the 
  outer 
  tooth 
  is 
  channeled, 
  the 
  coronal 
  ridge 
  of 
  

   all 
  the 
  individual 
  teeth 
  rises 
  into 
  a 
  turgid 
  sub-median 
  apex 
  nearest 
  

   the 
  postero-lateral 
  border 
  of 
  the 
  series, 
  slightly 
  concave 
  along 
  the 
  

   sloping 
  obtuse 
  crest 
  on 
  either 
  side 
  and 
  sharply 
  deflected 
  forward 
  at 
  

   the 
  extremities 
  into 
  a 
  sort 
  of 
  short 
  fold 
  ; 
  the 
  inner 
  margin 
  is 
  gently 
  

  

  -9 
  

  

  