﻿American 
  Ordovician 
  Lichadidce. 
  31 
  

  

  Lichas 
  (Hoplolichas) 
  bicomis 
  Ulrich, 
  PI. 
  II, 
  fig. 
  3, 
  from 
  

   the 
  Maquoketa 
  of 
  Minnesota. 
  

  

  Amphilichas 
  clermontensis 
  Slocom, 
  PI. 
  II, 
  fig. 
  7, 
  from 
  the 
  

   Maquoketa 
  of 
  Iowa. 
  

  

  Amphilichas 
  rhinoceras 
  Slocom, 
  PL 
  II, 
  fig. 
  4, 
  from 
  the 
  

   Maquoketa 
  of 
  Iowa. 
  

  

  Finally, 
  there 
  is 
  added 
  the 
  following 
  new 
  species, 
  

   Acrolichas 
  narrawayi, 
  known 
  only 
  from 
  the 
  pygidium; 
  

   the 
  addition 
  of 
  this 
  species 
  brings 
  the 
  total 
  described 
  

   forms 
  of 
  Acrolichas 
  up 
  to 
  thirteen. 
  

  

  Acrolichas 
  narrawayi 
  nov. 
  sp. 
  ; 
  pygidium 
  with 
  a 
  narrow 
  

   notch 
  between 
  the 
  free 
  tips 
  of 
  the 
  posterior 
  pair 
  of 
  ribs 
  ; 
  the 
  

   free 
  tips 
  of 
  all 
  ribs 
  are 
  rounded, 
  especially 
  in 
  case 
  of 
  the 
  

   posterior 
  pair; 
  furrow 
  limiting 
  posterior 
  margin 
  of 
  second 
  

   axial 
  ring 
  not 
  very 
  distinctly 
  defined. 
  From 
  a 
  quarry 
  at 
  

   Wright's 
  or 
  St. 
  Clovis' 
  dam, 
  near 
  Hull, 
  opposite 
  Ottawa, 
  

   Canada; 
  in 
  the 
  collection 
  of 
  James 
  E. 
  Narraway, 
  at 
  Ottawa. 
  

  

  5. 
  The 
  area 
  of 
  origin 
  of 
  Acrolichas. 
  

  

  Surely 
  there 
  must 
  be 
  some 
  significance 
  in 
  the 
  fact 
  

   that 
  twelve 
  species 
  of 
  Acrolichas 
  are 
  known 
  from 
  

   northern 
  America 
  and 
  only 
  one 
  species 
  from 
  Europe, 
  

   the 
  European 
  form 
  occurring 
  only 
  in 
  Ireland. 
  While 
  

   the 
  center 
  of 
  origin 
  of 
  the 
  Lichadidse 
  may 
  have 
  been 
  

   somewhere 
  near 
  the 
  Baltic 
  areas 
  of 
  northern 
  Europe, 
  

   judging 
  from 
  the 
  relative 
  number 
  of 
  generic 
  types 
  found 
  

   there 
  in 
  early 
  Ordovician 
  strata, 
  the 
  center 
  of 
  origin 
  of 
  

   the 
  American 
  genus 
  Acrolichas 
  must 
  have 
  been 
  nearer 
  

   the 
  North 
  American 
  continent. 
  The 
  number 
  of 
  Amer- 
  

   ican 
  species 
  of 
  Acrolichas 
  is 
  greater 
  than 
  the 
  twelve 
  here 
  

   listed. 
  When 
  the 
  forms 
  at 
  present 
  included 
  under 
  

   Lichas 
  minganensis, 
  Lichas 
  cucullus, 
  and 
  Lichas 
  harrisi 
  

   are 
  more 
  closely 
  discriminated, 
  at 
  least 
  iive 
  additional 
  

   species 
  will 
  become 
  known. 
  The 
  Irish 
  species, 
  Lichas 
  

   hibemicus, 
  probably 
  represents 
  some 
  migrant 
  from 
  

   American 
  waters. 
  Even 
  Murchison 
  noted 
  that 
  certain 
  

   American 
  genera 
  reached 
  Ireland 
  in 
  Llandeilo 
  times 
  

   without 
  extending 
  their 
  geographical 
  range 
  as 
  far 
  as 
  

   the 
  European 
  continent. 
  In 
  the 
  same 
  manner, 
  Acro- 
  

   lichas, 
  although 
  occurring 
  in 
  Ireland, 
  is 
  not 
  known 
  on 
  

   the 
  continent 
  of 
  Europe 
  itself, 
  unless 
  some 
  Baltic 
  forms, 
  

   at 
  present 
  referred 
  to 
  Amphilichas, 
  eventually 
  should 
  

   prove 
  to 
  be 
  typical 
  forms 
  of 
  Acrolichas. 
  

  

  