﻿American 
  Ordovician 
  Lichadidce. 
  33 
  

  

  and 
  then 
  widens 
  again 
  ; 
  moreover, 
  the 
  posterior 
  pair 
  of 
  

   lateral 
  ribs 
  bears 
  a 
  diagonal 
  furrow, 
  a 
  feature 
  unknown 
  

   in 
  Acrolichas. 
  This 
  association 
  of 
  glabella 
  and 
  pygi- 
  

   dium 
  in 
  the 
  genotype 
  of 
  Amphilichas 
  needs 
  verification. 
  

  

  7. 
  The 
  pygidia 
  of 
  Acrolichas 
  compared 
  with 
  those 
  of 
  Metalichas. 
  

  

  The 
  pygidia 
  of 
  Acrolichas 
  also 
  offer 
  an 
  illustration 
  of 
  

   parallelism. 
  Eaymond, 
  in 
  1910, 
  regarded 
  the 
  pygidium 
  

   of 
  Lichas 
  minganensis 
  as 
  similar 
  to 
  the 
  pygidium 
  as- 
  

   signed 
  by 
  Schmidt 
  to 
  Lichas 
  cicatrico 
  sus 
  (PL 
  IV, 
  fig. 
  4B, 
  

   of 
  present 
  paper). 
  Lichas 
  cicatricosus 
  Schmidt 
  (non 
  

   Loven) 
  is 
  the 
  genotype 
  of 
  Metalichas, 
  proposed 
  by 
  Eeed, 
  

   in 
  1902. 
  In 
  this 
  East 
  Baltic 
  species, 
  the 
  axial 
  lobe 
  of 
  

   the 
  pygidium 
  narrows 
  to 
  a 
  point 
  posteriorly, 
  and 
  the 
  

   posterior 
  pair 
  of 
  lateral 
  ribs 
  is 
  without 
  distinct 
  diagonal 
  

   furrows, 
  corresponding 
  in 
  this 
  respect 
  to 
  Acrolichas. 
  

   As 
  a 
  matter 
  of 
  fact, 
  the 
  similarity 
  is 
  greater 
  than 
  

   Schmidt's 
  figure 
  would 
  suggest, 
  since 
  in 
  the 
  accompany- 
  

   ing 
  text 
  Schmidt 
  states 
  that 
  there 
  is 
  a 
  diagonal 
  furrow 
  on 
  

   f^e 
  second 
  pair 
  of 
  ribs 
  as 
  well 
  as 
  on 
  the 
  first 
  pair, 
  

   .xthough 
  in 
  his 
  figure 
  no 
  trace 
  of 
  this 
  furrow 
  can 
  be 
  seen 
  

   on 
  either 
  one 
  of 
  this 
  second 
  pair 
  of 
  ribs. 
  This 
  feature 
  is 
  

   shown 
  better 
  by 
  Schmidt's 
  figure 
  of 
  the 
  pygidium 
  of 
  

   Lichas 
  St. 
  Mathim 
  (PL 
  IV, 
  fig. 
  5B 
  of 
  the 
  present 
  paper), 
  

   a 
  species 
  evidently 
  congeneric 
  with 
  Lichas 
  cicatricosus. 
  

   The 
  cranidia 
  of 
  Metalichas, 
  however, 
  differ 
  greatly 
  from 
  

   those 
  of 
  Acrolichas. 
  The 
  anterior 
  and 
  posterior 
  pairs 
  of 
  

   lateral 
  glabellar 
  lobes 
  are 
  distinctly 
  defined, 
  but 
  the 
  

   space 
  which 
  should 
  be 
  occupied 
  by 
  the 
  second 
  pair 
  of 
  

   lobes 
  is 
  not 
  even 
  faintly 
  limited 
  from 
  the 
  fixed 
  cheeks. 
  

  

  8. 
  The 
  pygidia 
  of 
  Acrolichas 
  compared 
  with 
  those 
  of 
  Platopo- 
  

  

  lichas. 
  

  

  The 
  pygidium 
  of 
  the 
  Bohemian 
  genus 
  Platopolichas, 
  

   proposed 
  by 
  GKirich 
  in 
  1901, 
  and 
  including 
  the 
  species 
  

   Lichas 
  avus 
  (PL 
  III, 
  fig. 
  7) 
  and 
  Lichas 
  incola 
  (PL 
  IV, 
  

   fig. 
  8), 
  both 
  described 
  by 
  Barrande 
  from 
  lower 
  Ordovi- 
  

   cian 
  strata, 
  is 
  similar 
  to 
  that 
  of 
  Acrolichas 
  in 
  having 
  no 
  

   diagonal 
  furrow 
  on 
  the 
  posterior 
  lateral 
  ribs, 
  andin 
  hav- 
  

   ing 
  the 
  narrowing 
  of 
  the 
  axial 
  lobe 
  continue 
  to 
  its 
  end, 
  

   but 
  it 
  differs 
  in 
  not 
  having 
  this 
  narrowing 
  of 
  the 
  axial 
  

   lobe 
  continue 
  until 
  the 
  latter 
  is 
  reduced 
  to 
  a 
  point 
  at 
  the 
  

  

  Am 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XLIX, 
  No. 
  289.— 
  January, 
  1920. 
  

  

  