﻿American 
  Ordovician 
  Lichadidce. 
  27 
  

  

  pair 
  of 
  lobes, 
  although 
  the 
  latter 
  are 
  not 
  differentiated 
  

   from 
  the 
  free 
  cheeks. 
  In 
  the 
  Corryville 
  species, 
  on 
  the 
  

   contrary, 
  the 
  posterior 
  pair 
  of 
  glabellar 
  lobes 
  is 
  distinctly 
  

   larger, 
  and 
  is 
  in 
  direct 
  contact 
  with 
  an 
  anterior 
  pair, 
  

   departing 
  in 
  this 
  respect 
  from 
  the 
  generic 
  type 
  of 
  Platy- 
  

   lichas. 
  The 
  reference 
  of 
  Lichas 
  halli 
  to 
  Platylichas 
  

   therefore 
  is 
  founded 
  on 
  resemblance 
  rather 
  than 
  on 
  strict 
  

   agreement, 
  in 
  structure 
  with 
  the 
  European 
  type. 
  

  

  The 
  pygidium 
  figured 
  by 
  the 
  writer 
  from 
  the 
  White- 
  

   water 
  member 
  of 
  the 
  Richmond, 
  at 
  Richmond, 
  Indiana 
  

   (Jour. 
  Cincinnati 
  Soc. 
  Nat. 
  Hist,, 
  22, 
  pi. 
  1, 
  fig. 
  2, 
  1917; 
  

   also 
  Plate 
  II, 
  fig. 
  10 
  in 
  present 
  paper), 
  resembles 
  that 
  of 
  

   Lichas 
  halli 
  in 
  the 
  presence 
  of 
  free 
  tips 
  on 
  all 
  the 
  ribs, 
  

   and 
  of 
  a 
  diagonal 
  furrow 
  on 
  each 
  of 
  the 
  posterior 
  ribs 
  ; 
  

   moreover, 
  the 
  axial 
  lobe 
  narrows 
  and 
  widens 
  again 
  pos- 
  

   teriorly. 
  Provisionally 
  this 
  pygidium 
  may 
  be 
  referred 
  

  

  A 
  B 
  

  

  Platylichas 
  margaritifer 
  Nieszkowski. 
  Genotype. 
  

  

  to 
  the 
  same 
  genus 
  as 
  Lichas 
  halli, 
  under 
  the 
  name 
  Platy- 
  

   lichas 
  (?) 
  miseneri 
  Nov. 
  sp. 
  In 
  the 
  absence 
  of 
  the 
  cra- 
  

   nidium, 
  however, 
  the 
  reference 
  of 
  this 
  pygidium 
  to 
  

   Platylichas 
  is 
  necessarily 
  more 
  uncertain 
  than 
  that 
  of 
  

   Lichas 
  halli, 
  of 
  which 
  the 
  entire 
  structure 
  is 
  known. 
  

  

  A 
  remarkable 
  pygidium 
  found 
  in 
  the 
  Kimmswick 
  lime- 
  

   stone 
  at 
  Cape 
  Girardeau, 
  Missouri, 
  PL 
  II, 
  fig. 
  9, 
  has 
  free 
  

   tips 
  at 
  the 
  ends 
  of 
  all 
  of 
  the 
  ribs, 
  the 
  posterior 
  pair 
  of 
  

   ribs 
  is 
  not 
  crossed 
  by 
  a 
  diagonal 
  furrow, 
  and 
  the 
  furrow 
  

   limiting 
  the 
  posterior 
  margin 
  of 
  the 
  second 
  axial 
  ring 
  

   dies 
  out 
  before 
  reaching 
  the 
  dorsal 
  furrows 
  outlining 
  the 
  

   sides 
  of 
  the 
  axial 
  lobe. 
  All 
  of 
  these 
  characteristics 
  are 
  

   found 
  also 
  in 
  all 
  species 
  of 
  Acrolichas. 
  But 
  the 
  axial 
  

   lobe 
  of 
  the 
  Cape 
  Girardeau 
  specimen 
  does 
  not 
  narrow 
  to 
  

   a 
  point 
  posteriorly, 
  as 
  in 
  Acrolichas; 
  on 
  the 
  contrary, 
  it 
  

   narrows 
  very 
  rapidly 
  at 
  about 
  mid-length 
  and 
  then 
  

   expands 
  slightly 
  at 
  about 
  one-third 
  of 
  the 
  length 
  of 
  the 
  

   pygidium 
  from 
  its 
  posterior 
  end. 
  Among 
  European 
  

   Lichadidae, 
  the 
  Cape 
  Girardeau 
  specimen 
  resembles 
  the 
  

   pygidium 
  of 
  Hoplolichas 
  tricuspidatus 
  Beyrich, 
  PI. 
  IV, 
  

  

  