﻿VEETEBKATES. 
  189 
  

  

  the 
  length. 
  Posterolateral 
  border 
  nearly 
  straight, 
  with 
  a 
  slight 
  

   oblique 
  course 
  outward 
  and 
  forward, 
  enamel 
  fold 
  narrow, 
  basal 
  por- 
  

   tion 
  relatively 
  deep, 
  slightly 
  channeled; 
  antero-lateral 
  border 
  con- 
  

   verging 
  toward 
  point 
  of 
  inrollment 
  at 
  a 
  moderate 
  angle 
  with 
  the 
  

   opposite 
  border, 
  the 
  relatively 
  deep 
  basal 
  rim 
  projecting 
  beyond 
  the 
  

   coronal 
  fold 
  ; 
  inner 
  margin 
  gently 
  arched 
  from 
  the 
  rounded 
  posterior 
  

   angle, 
  with 
  a 
  slight 
  sigmoidal 
  curvature 
  in 
  passing 
  to 
  the 
  subacute 
  

   anterior 
  angle 
  ; 
  as 
  usual 
  the 
  edge 
  is 
  interiorly 
  beveled. 
  Crown 
  sur- 
  

   face 
  very 
  gently 
  and 
  uniformly 
  convex 
  transversely, 
  the 
  enameled 
  

   inner 
  portion 
  showing 
  transverse 
  imbrications 
  or 
  lines 
  of 
  growth 
  

   parallel 
  with 
  the 
  inner 
  margin, 
  with 
  the 
  usual 
  delicate 
  rugose 
  

   appearance, 
  beneath 
  which 
  the 
  tubular 
  structure 
  is 
  discernible, 
  and 
  

   which 
  in 
  worn 
  surfaces 
  assumes 
  the 
  minute, 
  closely 
  arranged 
  punc- 
  

   tate 
  character. 
  Greatest 
  transverse 
  diameter 
  across 
  inner 
  margin, 
  

   13 
  mm. 
  ; 
  length 
  along 
  postero-lateral 
  border 
  to 
  point 
  of 
  inrollment, 
  

   about 
  8 
  mm. 
  

  

  The 
  form 
  above 
  described 
  is 
  represented 
  by 
  a 
  solitary 
  specimen, 
  

   in 
  the 
  collection 
  of 
  Mr. 
  Van 
  Home. 
  The 
  tooth 
  is 
  in 
  good 
  preserva- 
  

   tion, 
  save 
  that 
  the 
  outer 
  margin 
  has 
  been 
  entirely 
  worn 
  away, 
  

   presenting 
  a 
  thick, 
  blunt 
  emarginate 
  edge, 
  the 
  inrolled 
  extremity 
  

   on 
  the 
  posterior 
  side 
  being 
  much 
  more 
  worn 
  than 
  at 
  the 
  opposite 
  

   side. 
  The 
  inferior 
  surface 
  of 
  the 
  tooth, 
  however, 
  plainly 
  shows 
  the 
  

   direction 
  of 
  the 
  oblique 
  inrollment, 
  as 
  indicated 
  by 
  the 
  course 
  of 
  the 
  

   longitudinal 
  striation. 
  The 
  form 
  agrees 
  in 
  all 
  essential 
  particulars 
  

   with 
  the 
  homologous 
  teeth 
  noticed 
  in 
  connection 
  with 
  Sandalodus 
  

   complanatus, 
  and 
  S. 
  l<zvissimus 
  ; 
  at 
  the 
  same 
  time 
  it 
  also 
  agrees, 
  in 
  the 
  

   character 
  of 
  the 
  surface 
  punctation 
  and 
  the 
  delicate 
  rugose 
  mark- 
  

   ings 
  of 
  the 
  enamel 
  layer, 
  with 
  the 
  other 
  forms 
  of 
  the 
  species 
  to 
  

   which 
  we 
  have 
  referred 
  it. 
  However, 
  in 
  the 
  supposed 
  associate 
  

   forms 
  we 
  have 
  failed 
  to 
  detect 
  the 
  presence 
  of 
  transverse 
  lines 
  of 
  

   growth, 
  such 
  as 
  constitute 
  a 
  marked 
  feature 
  in 
  the 
  enamel 
  layer 
  of 
  

   the 
  present 
  form. 
  The 
  uniform 
  transverse 
  convexity 
  of 
  the 
  coronal 
  

   region 
  and 
  its 
  outline 
  readily 
  distinguish 
  the 
  present 
  tooth 
  from 
  its 
  

   congeneric 
  allies. 
  

  

  Eeferring 
  to 
  the 
  synonymy 
  it 
  will 
  be 
  observed 
  that 
  the 
  form 
  orig- 
  

   inally 
  described 
  under 
  the 
  name 
  Deltodus 
  rhomboideus, 
  N. 
  and 
  W., 
  

   is 
  transferred 
  to 
  the 
  specific 
  category 
  embracing 
  the 
  form 
  first 
  

   noticed 
  under 
  the 
  term 
  Sandalodus 
  spatulatus, 
  the 
  two 
  forms 
  respec- 
  

   tively 
  representing 
  the 
  supposed 
  posterior 
  teeth 
  of 
  the 
  lower 
  and 
  

   upper 
  jaws 
  of 
  the 
  same 
  species. 
  These 
  forms 
  most 
  intimately 
  agree 
  

   in 
  the 
  details 
  of 
  coronal 
  structure, 
  while 
  they 
  differ 
  one 
  from 
  the 
  

  

  