﻿VEETEBBATES. 
  93 
  

  

  Deltoptychius 
  primus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  V. 
  Fig. 
  6-8. 
  

  

  The 
  dentition 
  of 
  the 
  earliest 
  known 
  species 
  of 
  Deltoptychius 
  is 
  

   represented 
  in 
  the 
  collections 
  by 
  a 
  few 
  imperfect, 
  fragmentary 
  exam- 
  

   ples 
  of 
  the 
  posterior 
  forms 
  of 
  the 
  upper 
  and 
  lower 
  jaws, 
  which 
  

   attain 
  medium 
  size. 
  The 
  mandibular 
  teeth 
  may 
  be 
  distinguished 
  in 
  

   the 
  examples 
  before 
  us 
  by 
  the 
  obscurer 
  definition 
  of 
  the 
  median 
  

   prominence 
  from 
  the 
  narrow 
  belt 
  in 
  front, 
  and 
  shallow 
  depth 
  of 
  the 
  

   enameled 
  abrupt 
  antero-lateral 
  border. 
  The 
  opposed 
  teeth 
  of 
  the 
  

   upper 
  jaw 
  appear 
  to 
  have 
  had 
  the 
  principal 
  posterior 
  prominence 
  

   relatively 
  more 
  convex 
  transversely, 
  producing 
  a 
  more 
  rounded 
  out- 
  

   line 
  in 
  this 
  part 
  of 
  the 
  inner 
  margin 
  than 
  obtains 
  in 
  the 
  repre- 
  

   sentative 
  Keokuk 
  species. 
  In 
  the 
  proportionate 
  prominence 
  of 
  the 
  

   secondary 
  lobe, 
  the 
  present 
  teeth 
  bear 
  greater 
  resemblance 
  to 
  the 
  

   corresponding 
  form 
  occurring 
  in 
  the 
  Warsaw 
  limestone, 
  from 
  which, 
  

   however, 
  they 
  differ 
  in 
  the 
  greater 
  convexity 
  of 
  the 
  posterior 
  promi- 
  

   nence. 
  In 
  size 
  the 
  above 
  noticed 
  teeth 
  are 
  uniformly 
  below 
  that 
  

   attained 
  by 
  the 
  allied 
  forms 
  in 
  the 
  Keokuk 
  limestone, 
  holding 
  in 
  

   this 
  particular 
  an 
  intermediate 
  position 
  between 
  the 
  latter 
  and 
  the 
  

   Warsaw 
  species. 
  

  

  The 
  examples 
  of 
  the 
  above 
  noticed 
  forms 
  thus 
  far 
  known, 
  chiefly 
  

   from 
  discoveries 
  of 
  Mr. 
  Springer 
  and 
  Mr. 
  Wachsmuth, 
  are 
  few, 
  and 
  

   unfortunately 
  in 
  a 
  very 
  imperfect 
  state 
  of 
  preservation, 
  owing 
  to 
  the 
  

   friable 
  nature 
  of 
  the 
  mineralized 
  dental 
  substance; 
  and 
  while 
  the 
  

   material 
  is 
  insufficient 
  to 
  enable 
  a 
  detailed 
  description 
  of 
  the 
  teeth, 
  it 
  

   affords 
  ample 
  evidence 
  of 
  the 
  generic 
  relations, 
  as 
  also 
  indicating 
  

   the 
  characteristics 
  by 
  which 
  they 
  may 
  be 
  contrasted 
  with 
  congeneric 
  

   forms. 
  

  

  Geological 
  position 
  and 
  localities: 
  Upper 
  Burlington 
  fish-bed 
  ; 
  Buf- 
  

   fington 
  creek, 
  and 
  Augusta, 
  Iowa. 
  

  

  Deltoptychius 
  Wachsmuthi, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  V, 
  Fig. 
  1-5. 
  

  

  Teeth, 
  attaining 
  medium 
  size. 
  Mandibular 
  posterior 
  form 
  triangu- 
  

   lar 
  in 
  outline, 
  sigmoidally 
  curved 
  along 
  the 
  inner 
  margin, 
  terminating 
  

   in 
  front 
  in 
  a 
  narrow, 
  inrolled 
  beak 
  ; 
  postero-lateral 
  border 
  gradually 
  

   converging 
  toward 
  the 
  outer 
  extremity, 
  showing 
  a 
  deep, 
  nearly 
  vertical 
  

   basal 
  border, 
  slightly 
  inclined 
  outward, 
  and 
  expanded 
  toward 
  the 
  

  

  