﻿VERTEBRATES. 
  163 
  

  

  punctation 
  and 
  undulations 
  and 
  the 
  delicate 
  transverse 
  tracery 
  

   observed 
  in 
  partially 
  exfoliated 
  surfaces, 
  especially 
  of 
  the 
  wing 
  ex- 
  

   pansion. 
  A 
  specimen 
  of 
  the 
  ordinary 
  size 
  measures 
  in 
  extreme 
  

   length 
  along 
  the 
  coronal 
  crest 
  23 
  mm; 
  antero-lateral 
  border 
  about 
  16 
  

   mm; 
  breadth 
  across 
  inner 
  margin 
  8 
  mm. 
  

  

  The 
  present 
  species 
  is 
  of 
  peculiar 
  interest 
  on 
  account 
  of 
  the 
  

   facts 
  it 
  affords 
  in 
  relation 
  to 
  specific 
  diferentiation 
  and 
  the 
  inti- 
  

   mate 
  resemblances 
  that 
  exist 
  between 
  the 
  individuals 
  of 
  allied 
  

   species. 
  Thus, 
  compared 
  with 
  the 
  Chester 
  form 
  there 
  exists 
  mark- 
  

   edly 
  close 
  resemblance 
  between 
  the 
  mandibular 
  posterior 
  teeth, 
  the 
  

   chief 
  distinction 
  in 
  the 
  present 
  form 
  being 
  its, 
  perhaps, 
  less 
  oblique 
  

   inner 
  margin, 
  the 
  peculiar 
  coronal 
  ornamentation 
  and 
  less 
  regular 
  

   punctate 
  structure." 
  But 
  in 
  relation 
  to 
  the 
  maxillary 
  posterior 
  teeth 
  

   of 
  the 
  two 
  forms, 
  a 
  marked 
  difference 
  is 
  apparent, 
  the 
  present 
  form 
  

   being 
  relatively 
  much 
  more 
  elongate 
  longitudinally 
  and 
  proportion- 
  

   ately 
  narrower, 
  while 
  the 
  proportionately 
  narrow, 
  plane 
  or 
  slightly 
  

   convex 
  anterior 
  elope 
  contracts 
  with 
  the 
  wide, 
  gently 
  concave 
  -^ 
  

   declivity 
  characteristic 
  of 
  the 
  Chester 
  teeth. 
  

  

  Geological 
  position 
  and 
  localities: 
  St. 
  Louis 
  formation; 
  Pella, 
  

   Iowa, 
  Alton 
  and 
  other 
  localities 
  in 
  Madison 
  and 
  Monroe 
  counties, 
  

   Black's 
  Hill, 
  Hardin 
  Co., 
  111., 
  St. 
  Louis, 
  Mo. 
  

  

  Deltodopsis 
  angustus, 
  (N. 
  and 
  W., 
  sp.) 
  

  

  PL 
  XI, 
  Fig. 
  7-10. 
  

   Beltodus 
  angustus, 
  Newbeeey 
  and 
  Woethen, 
  1870, 
  111. 
  Geol. 
  Surv. 
  IV, 
  p. 
  368, 
  PI. 
  Hi, 
  f. 
  7. 
  

  

  Maxillary 
  posterior 
  teeth 
  subcuneate 
  in 
  outline, 
  very 
  moderately 
  

   arched 
  longitudinally, 
  except 
  at 
  the 
  inrolled 
  extremity. 
  The 
  antero- 
  

   lateral 
  articular 
  border 
  comprising 
  somewhat 
  more 
  than 
  half 
  the 
  

   extreme 
  length 
  of 
  the 
  tooth, 
  defined 
  by 
  the 
  thick, 
  rounded 
  enamel 
  

   fold, 
  which 
  is 
  strongly 
  inbeveled 
  to 
  the 
  shallow, 
  channeled 
  basal 
  

   rim; 
  inner 
  margin 
  very 
  obliquely 
  produced 
  backward 
  from 
  the 
  ob- 
  

   tuse 
  anterior 
  angle, 
  where 
  it 
  unites 
  with 
  the 
  antero-lateral 
  border, 
  

   sharply 
  arched 
  round 
  the 
  base 
  of 
  the 
  coronal 
  ridge, 
  with 
  a 
  slight 
  

   sigmoidal 
  curvature 
  thence 
  to 
  the 
  posterior 
  angle 
  nearly 
  at 
  right- 
  

   angles 
  to 
  the 
  anterior 
  portion; 
  postero-lateral 
  border 
  gently 
  curved 
  

   from 
  a 
  right 
  line, 
  very 
  gradually 
  converging 
  toward 
  the 
  inrolled 
  ex- 
  

   tremity^ 
  coronal 
  enamel 
  forming 
  a 
  very 
  narrow, 
  inbeveled 
  fold, 
  well 
  

   defined 
  from 
  the 
  shallow-channeled 
  deep 
  basal 
  border, 
  which 
  is 
  

   usually 
  inbeveled, 
  — 
  probably 
  in 
  perfect 
  specimens 
  nearly 
  vertical, 
  

  

  