﻿VEETEBEATES. 
  165 
  

  

  The 
  dozen 
  or 
  so 
  examples 
  of 
  each 
  of 
  the 
  above 
  described 
  forms 
  

   contained 
  in 
  the 
  collections, 
  offer 
  facilities 
  for 
  acquiring 
  a 
  somewhat 
  

   comprehensive 
  understanding 
  of 
  their 
  characteristic 
  features, 
  which 
  

   are 
  remarkable 
  for 
  their 
  persistency, 
  the 
  individuals 
  presenting 
  com- 
  

   paratively 
  slight 
  variation 
  among 
  themselves. 
  Although 
  associated 
  

   in 
  the 
  same 
  strata, 
  in 
  every 
  instance 
  thus 
  far 
  observed 
  the 
  teeth 
  

   occur 
  as 
  isolated 
  specimens 
  disconnected 
  from 
  their 
  original 
  position 
  

   in 
  relation 
  to 
  one 
  another. 
  Therefore, 
  in 
  regard 
  to 
  the 
  assumed 
  

   specific 
  identity 
  of 
  the 
  forms 
  here 
  alluded 
  to, 
  the 
  presumptive 
  evi- 
  

   dence 
  is 
  precisely 
  the 
  same 
  as 
  allowed 
  in 
  the 
  association 
  of 
  forms 
  

   in 
  other 
  specific 
  groups, 
  the 
  justification 
  of 
  which 
  is 
  derived 
  from 
  

   what 
  is 
  known 
  in 
  relation 
  to 
  the 
  diverse 
  dentition 
  of 
  Cochliodus. 
  In 
  

   the 
  present 
  species, 
  however, 
  we 
  are 
  as 
  yet 
  unable 
  to 
  determine 
  the 
  

   character 
  of 
  the 
  teeth 
  holding 
  anterior 
  positions 
  upon 
  the 
  jaws. 
  In 
  

   the 
  case 
  of 
  the 
  mandibular 
  terminal 
  or 
  posterior 
  teeth, 
  the 
  relatively 
  

   short 
  articular 
  border 
  necessitates 
  a 
  corresponding 
  abbreviated 
  longi- 
  

   tudinal 
  diameter 
  for 
  the 
  tooth 
  immediately 
  in 
  advance 
  ; 
  and 
  so, 
  also, 
  

   as 
  regards 
  the 
  maxillary 
  teeth, 
  which 
  latter 
  may 
  have 
  been 
  associ- 
  

   ated 
  with 
  teeth 
  whose 
  form 
  bears 
  the 
  remotest 
  suggestion 
  of 
  their 
  

   relationship 
  with 
  the 
  teeth 
  described. 
  

  

  Geological 
  position 
  and 
  locality 
  : 
  Chester 
  limestone, 
  Chester 
  ; 
  and 
  

   near 
  Columbia, 
  Monroe 
  county, 
  Illinois. 
  

  

  Deltodopsis? 
  convoluttjs, 
  St. 
  J. 
  and 
  W. 
  

  

  PL 
  XI, 
  Fig. 
  11-12. 
  

  

  Teeth 
  obliquely 
  subtrigonal 
  in 
  outline, 
  strongly 
  arched 
  from 
  within 
  

   outward, 
  with 
  strong 
  spiral 
  inrollment. 
  Antero-lateral 
  border 
  making 
  

   a 
  gentle 
  sigmoidal 
  curvature 
  in 
  its 
  slightly 
  oblique 
  forward 
  and 
  out- 
  

   ward 
  course, 
  basal 
  portion 
  very 
  deep, 
  broadly 
  channeled, 
  terminat- 
  

   ing 
  below 
  in 
  a 
  narrow 
  rim, 
  and 
  bordered 
  above 
  by 
  the 
  rounded, 
  

   inbeveled 
  enamel 
  fold 
  which 
  constitutes 
  about 
  one-third 
  the 
  height 
  

   of 
  the 
  border; 
  postero-lateral 
  border 
  converging 
  at 
  a 
  variable 
  angle 
  

   of 
  50° 
  to 
  70°, 
  mature 
  individuals 
  being 
  relatively 
  narrower* 
  than 
  

   medium, 
  and 
  small-sized 
  teeth, 
  obliquity 
  somewhat 
  greater 
  tban 
  

   that 
  of 
  the 
  opposite 
  side, 
  basal 
  portion 
  deep 
  and 
  rather 
  deeply 
  chan- 
  

   neled, 
  the 
  lower 
  edge 
  expanding 
  posteriorly 
  beyond 
  the 
  rounded, 
  

   inbeveled 
  enamel 
  fold, 
  which 
  envelopes 
  the 
  upper 
  third 
  of 
  the 
  height 
  

   of 
  the 
  border 
  ; 
  inner 
  margin 
  making 
  a 
  slight 
  sigmoidal 
  curvature 
  

   from 
  the 
  obtuse 
  anterior 
  angle 
  to 
  the 
  base 
  of 
  the 
  coronal 
  ridge 
  

  

  