﻿VEBTEBEATES. 
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  site 
  side 
  abruptly 
  descending 
  into 
  the 
  deep 
  posterior 
  depression, 
  

   alate 
  lobe 
  somewhat 
  steeply 
  upraised 
  and 
  relatively 
  wide, 
  trans- 
  

   versely 
  convex 
  and 
  thickened 
  along 
  the 
  border. 
  The 
  superficial 
  

   transverse 
  rug* 
  show 
  strongest 
  development 
  in 
  the 
  anterior 
  slope 
  

   and 
  the 
  posterior 
  wing, 
  in 
  the 
  latter 
  region 
  being 
  nearly 
  at 
  right 
  

   angles 
  to 
  their 
  course 
  in 
  the 
  former 
  space, 
  where, 
  in 
  some 
  examples, 
  

   at 
  least, 
  the 
  surface 
  is 
  marked 
  by 
  stronger 
  rugosities 
  descending 
  

   from 
  the 
  crest 
  of 
  the 
  median 
  ridge. 
  Surface 
  punctse 
  the 
  same 
  as 
  

   described 
  in 
  the 
  opposed 
  maxillary 
  teeth. 
  A 
  specimen 
  below 
  medium 
  

   size 
  measures 
  across 
  the 
  inner 
  margin 
  15 
  mm. 
  ; 
  length 
  along 
  antero- 
  

   lateral 
  border 
  to 
  point 
  of 
  inrollment 
  9 
  mm. 
  

  

  Only 
  the 
  posterior 
  teeth 
  of 
  the 
  upper 
  and 
  lower 
  jaws 
  of 
  the 
  pres- 
  

   ent 
  species 
  have 
  been 
  identified, 
  represented 
  by 
  half 
  a 
  dozen 
  

   individuals 
  of 
  each 
  form, 
  and 
  these, 
  with 
  one 
  or 
  two 
  exceptions, 
  in 
  

   the 
  usual 
  fragmentary 
  state 
  of 
  preservation. 
  Compared 
  with 
  the 
  

   forms 
  of 
  the 
  species 
  with 
  which 
  they 
  are 
  associated, 
  C. 
  rugosus, 
  

   (N. 
  and 
  W. 
  sp.), 
  the 
  maxillary 
  teeth 
  are 
  distinguishable 
  by 
  the 
  rel- 
  

   ative 
  greater 
  prominence 
  of 
  the 
  posterior 
  lobe, 
  the 
  verrucose 
  orna- 
  

   mentation 
  of 
  the 
  anterior 
  lobe, 
  and, 
  perhaps, 
  the 
  course 
  of 
  the 
  

   transverse 
  rugae 
  in 
  the 
  region 
  of 
  the 
  median 
  depression. 
  The 
  man- 
  

   dibular 
  teeth 
  also 
  differ 
  in 
  the 
  relative 
  prominence^ 
  the 
  sharply 
  

   rounded 
  crest 
  of 
  the 
  median 
  lobe, 
  depth 
  of 
  posterior 
  depression, 
  

   proportionately 
  greater 
  breadth 
  of 
  the 
  alate 
  lobe, 
  and 
  more 
  robust 
  

   build. 
  In 
  some 
  of 
  the 
  features 
  contrasting 
  with 
  the 
  associate 
  species 
  

   there 
  are 
  more 
  intimate 
  resemblances 
  with 
  the 
  Upper 
  Burlington 
  

   species, 
  C 
  Springeri, 
  especially 
  as 
  regards 
  the 
  mandibular 
  posterior 
  

   teeth; 
  but 
  the 
  maxillary 
  teeth 
  of 
  the 
  latter, 
  again, 
  are 
  more 
  like 
  

   those 
  of 
  C. 
  rugosus, 
  though 
  they 
  are 
  not 
  to 
  be 
  confounded 
  with 
  that 
  

   species. 
  

  

  Geological 
  position 
  and 
  localities: 
  Keokuk 
  limestone, 
  main 
  fish-bed 
  

   horizon; 
  Keokuk, 
  Bentonsport 
  (Iowa), 
  Hamilton, 
  Warsaw, 
  Nauvoo 
  

   and 
  Scott 
  county 
  (Illinois). 
  

  

  Chitonodus 
  lieatus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  VI, 
  Fig. 
  1. 
  

  

  The 
  present 
  species 
  is 
  represented 
  by 
  a 
  solitary 
  imperfect 
  exam- 
  

   ple 
  of 
  a 
  maxillary 
  posterior 
  tooth, 
  showing 
  the 
  anterior 
  portion, 
  the 
  

   posterior 
  lobe 
  having 
  been 
  destroyed. 
  The 
  part 
  preserved, 
  however, 
  

   indicates 
  a 
  tooth 
  of 
  small 
  size, 
  with 
  a 
  diameter 
  across 
  the 
  inner 
  

   margin 
  probably 
  not 
  exceeding 
  13 
  mm., 
  with 
  a 
  length 
  along 
  the 
  

  

  

  7 
  

  

  