﻿192 
  Twenty-eighth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  The 
  distinguishing 
  features 
  of 
  the 
  genus 
  Ckyph^etts 
  of 
  

   Green 
  (1837), 
  are, 
  according 
  to 
  its 
  author, 
  the 
  fimbriate 
  caudal 
  

   shield, 
  of 
  which 
  he 
  remarks 
  : 
  ' 
  ' 
  The 
  second 
  series 
  of 
  ribs, 
  

   which 
  proceed 
  beyond 
  the 
  costal 
  arches 
  of 
  the 
  Cryphseus, 
  

   we 
  suppose 
  will 
  distinguish 
  it 
  from 
  every 
  other 
  described 
  

   genus." 
  He 
  remarks 
  that 
  "a 
  very 
  slight 
  obliteration" 
  of 
  

   these 
  parts 
  " 
  would 
  give 
  them 
  all 
  the 
  characters 
  of 
  a 
  Caly- 
  

   mene 
  " 
  =Phacops. 
  

  

  In 
  considering 
  the 
  question 
  of 
  generic 
  identity, 
  however, 
  

   it 
  should 
  not 
  be 
  forgotten 
  that 
  the 
  typical 
  forms 
  of 
  the 
  genus 
  

   Dalmanites, 
  which 
  are 
  similar 
  to 
  the 
  Magara 
  and 
  lower 
  

   Helderberg 
  species, 
  have 
  never 
  shown 
  the 
  denticulated 
  anterior 
  

   border 
  or 
  fimbriated 
  pygidium. 
  The 
  genus 
  was 
  originally 
  

   characterized 
  as 
  having 
  many 
  annulations 
  in 
  the 
  axis 
  of 
  the 
  

   pygidium, 
  but 
  farther 
  investigation 
  has 
  included 
  forms 
  with 
  

   few 
  annulations. 
  The 
  Odontocephaltts, 
  in 
  its 
  typical 
  form, 
  

   is 
  characterized 
  by 
  the 
  denticulate 
  border 
  and 
  a 
  pygidium 
  

   with 
  few 
  annulations 
  in 
  the 
  axis. 
  Similar 
  characteristics 
  mark 
  

   the 
  other 
  allied 
  species, 
  so 
  far 
  as 
  known. 
  

  

  Whatever 
  may 
  be 
  the 
  real 
  value 
  or 
  importance 
  of 
  these 
  

   structural 
  modifications, 
  it 
  is 
  interesting 
  to 
  find 
  their 
  manifes- 
  

   tation 
  coincident 
  with 
  the 
  change 
  or 
  succession 
  of 
  the 
  geolog- 
  

   ical 
  formations. 
  The 
  lowest 
  forms, 
  geologically, 
  have 
  simple 
  

   phacopidean 
  heads 
  — 
  (the 
  posterior 
  angles 
  not 
  produced) 
  with 
  

   pygidia 
  which 
  are 
  acute 
  or 
  subacute 
  posteriorly 
  and 
  have 
  

   numerous 
  annulations 
  in 
  the 
  axis. 
  In 
  the 
  next 
  phase 
  these 
  

   forms 
  of 
  the 
  group 
  have 
  the 
  posterior 
  angles 
  of 
  the 
  buckler 
  

   prolonged 
  into 
  spinform 
  extensions, 
  and 
  the 
  caudal 
  extrem- 
  

   ity 
  very 
  acute 
  or 
  extended 
  into 
  a 
  more 
  or 
  less 
  elongate 
  spine. 
  

   A 
  still 
  farther 
  modification 
  occurs 
  in 
  the 
  next 
  horizon 
  where 
  

   the 
  posterior 
  angles 
  of 
  the 
  buckler 
  are 
  extremely 
  prolonged, 
  

   the 
  caudal 
  extremity 
  extended 
  into 
  a 
  long 
  spine, 
  and 
  the 
  an- 
  

   terior 
  border 
  of 
  the 
  head 
  produced 
  into 
  a 
  simple 
  or 
  bifurcate, 
  

   or 
  sometimes 
  tridentate 
  process. 
  In 
  the 
  next 
  geological 
  period, 
  

   we 
  find 
  the 
  forms 
  of 
  this 
  group 
  having 
  the 
  posterior 
  angles 
  

   of 
  the 
  buckler 
  either 
  moderately 
  or 
  extremely 
  prolonged, 
  the 
  

   caudal 
  extremity 
  truncate 
  or 
  emarginate 
  (concave) 
  and 
  

   produced 
  on 
  each 
  side 
  posteriorly 
  into 
  a 
  short 
  spine 
  (or 
  some- 
  

   times 
  with 
  an 
  accessary 
  spine), 
  on 
  each 
  side, 
  and 
  the 
  extremi- 
  

   ties 
  of 
  the 
  caudal 
  ribs 
  spiniferous. 
  The 
  anterior 
  margin 
  of 
  

   the 
  buckler 
  is 
  rounded 
  or 
  slightly 
  produced 
  and 
  denticulate, 
  

   either 
  in 
  the 
  front 
  alone 
  or 
  upon 
  the 
  entire 
  border. 
  

  

  In 
  the 
  next 
  stage 
  the 
  anterior 
  margin 
  of 
  the 
  buckler 
  is 
  

   rounded 
  and 
  simple, 
  the 
  posterior 
  angles 
  more 
  or 
  less 
  pro- 
  

   longed 
  into 
  spiniform 
  extensions, 
  and 
  the 
  caudal 
  extremity 
  

   fimbriate 
  with 
  rounded 
  or 
  more 
  or 
  less 
  flattened 
  spiniform 
  

   processes 
  ; 
  of 
  these 
  there 
  are 
  five 
  on 
  each 
  side 
  of 
  the 
  axial 
  

   extremity, 
  which 
  is 
  likewise 
  produced 
  into 
  a 
  short 
  flattened 
  

   spine. 
  

  

  