﻿1864.] 
  SALTER 
  LINGULA-FLAG 
  FOSSILS. 
  235 
  

  

  which 
  is 
  considerably 
  oblique, 
  and 
  reaches 
  the 
  hinder 
  margin 
  just 
  at 
  

   the 
  base 
  of 
  the 
  spine 
  in 
  all 
  the 
  pleurae. 
  But 
  from 
  the 
  eighth 
  or 
  

   ninth 
  segments 
  the 
  pleurae 
  lengthen 
  and 
  the 
  axis 
  gradually 
  tapers. 
  

   The 
  hindmost 
  axial 
  ring 
  is 
  about 
  half 
  the 
  width 
  of 
  those 
  in 
  front, 
  

   and 
  scarcely 
  one-fourth 
  as 
  wide 
  as 
  its 
  long 
  pointed 
  pleurae. 
  

  

  All 
  the 
  middle 
  pleurae 
  have 
  a 
  strong 
  curve 
  backwards 
  from 
  the 
  

   fulcral 
  point, 
  but 
  at 
  the 
  same 
  time 
  arch 
  outwards, 
  and 
  gradually, 
  as 
  

   they 
  approach 
  the 
  tail, 
  close 
  in 
  upon 
  it 
  until 
  the 
  hindmost 
  are 
  par- 
  

   allel 
  with 
  it. 
  These 
  hinder 
  pleurae 
  are 
  greatly 
  lengthened, 
  and 
  are 
  

   of 
  two 
  forms 
  in 
  two 
  distinct 
  varieties 
  (possibly 
  sexes 
  ?). 
  In 
  one 
  form 
  

   (fig. 
  3) 
  the 
  penultimate 
  pleura 
  is 
  developed 
  into 
  a 
  shorter 
  spine 
  

   than 
  the 
  preceding, 
  and 
  the 
  last 
  is 
  suddenly 
  abbreviated 
  and 
  in- 
  

   curved. 
  This 
  may 
  be 
  by 
  abortion 
  of 
  the 
  segments. 
  In 
  another 
  the 
  

   increment 
  is 
  regular, 
  but 
  the 
  last 
  spines 
  are 
  not 
  extravagantly 
  deve- 
  

   loped. 
  In 
  a 
  third 
  variety 
  the 
  ultimate 
  and 
  penultimate 
  pleurae 
  are 
  

   greatly 
  extended 
  (fig. 
  2), 
  and 
  this 
  is 
  accompanied 
  by 
  a 
  corresponding 
  

   dilatation 
  and 
  lengthening 
  of 
  the 
  caudal 
  portion 
  next 
  to 
  be 
  described. 
  

  

  The 
  tail 
  in 
  this 
  species 
  (fig. 
  2a) 
  is 
  most 
  remarkable, 
  and 
  for 
  some 
  

   time 
  I 
  was 
  inclined 
  to 
  believe 
  that 
  its 
  outer 
  segment 
  was 
  the 
  ulti- 
  

   mate 
  pleura 
  of 
  the 
  body. 
  In 
  fact, 
  the 
  front 
  caudal 
  ring 
  is 
  a 
  slightly 
  

   metamorphosed 
  body 
  -joint, 
  and 
  is 
  not 
  very 
  strongly 
  connected 
  with 
  

   the 
  tail-piece 
  ; 
  but 
  it 
  nevertheless 
  belongs 
  to 
  it. 
  

  

  The 
  tail, 
  exclusive 
  of 
  the 
  great 
  sabre-shaped 
  lateral 
  spines, 
  which 
  

   are 
  three 
  or 
  four 
  times 
  its 
  length, 
  is 
  an 
  oblong 
  convex 
  plate, 
  with 
  a 
  

   short 
  conical 
  broad 
  axis 
  occupying 
  about 
  two-thirds 
  of 
  its 
  length, 
  and 
  

   annulated 
  by 
  two 
  or 
  three 
  incomplete 
  rings. 
  The 
  extremity 
  of 
  this 
  

   plate 
  is 
  broad 
  and 
  sharply 
  truncate, 
  contrasting 
  with 
  the 
  parabolic 
  

   contour 
  of 
  its 
  axis, 
  which 
  is 
  not 
  so 
  long 
  as 
  broad. 
  The 
  sabre-shaped 
  

   appendages 
  are 
  broader 
  as 
  well 
  as 
  longer 
  than 
  the 
  last 
  pleura 
  of 
  the 
  

   body-rings, 
  and 
  bend 
  inward 
  strongly 
  at 
  first 
  beneath 
  the 
  tail, 
  after- 
  

   wards 
  diverging 
  again 
  at 
  the 
  tips. 
  In 
  this 
  variety 
  (fig. 
  2) 
  they 
  are, 
  

   in 
  a 
  moderate-sized 
  specimen, 
  four 
  inches 
  long. 
  They 
  are 
  connate 
  

   with 
  the 
  central 
  plate 
  of 
  the 
  tail, 
  though 
  separated 
  from 
  it 
  by 
  a 
  deep 
  

   groove, 
  except 
  at 
  the 
  actual 
  base, 
  where 
  the 
  character 
  of 
  a 
  pleura 
  is 
  

   maintained 
  by 
  the 
  usual 
  pleural 
  groove 
  running 
  out 
  into 
  it. 
  The 
  

   nearest 
  approach 
  to 
  this 
  structure 
  is 
  made 
  by 
  the 
  Paradox 
  ides 
  

   Bohemicus. 
  But 
  in 
  that 
  species 
  the 
  enlarged 
  hinder 
  appendages 
  are 
  

   true 
  pleurae, 
  according 
  to 
  Barrande's 
  figure, 
  and 
  the 
  tail 
  itself 
  is 
  

   destitute 
  of 
  all 
  appendages. 
  Moreover, 
  in 
  that 
  allied 
  form 
  the 
  

   second 
  pleura 
  of 
  the 
  body 
  is 
  enlarged 
  ; 
  so 
  we 
  have 
  additional 
  cha- 
  

   racters 
  for 
  the 
  separation 
  of 
  the 
  present 
  species. 
  

  

  Paradoxides 
  Davidis 
  nearly 
  equals 
  in 
  dimensions 
  the 
  great 
  P. 
  

   Harlani 
  from 
  Massachusetts, 
  and 
  exceeds 
  the 
  large 
  Newfoundland 
  

   species 
  described 
  by 
  me 
  under 
  the 
  name 
  of 
  P. 
  Bennettii 
  *. 
  

  

  Locality, 
  Lower 
  Lingula-flags, 
  of 
  Porth-y-Rhaw 
  and 
  Solva 
  Har- 
  

   bour, 
  both 
  near 
  St. 
  David's, 
  South 
  Wales. 
  

  

  With 
  P. 
  Davidis, 
  which 
  is 
  really 
  a 
  common 
  fossil 
  at 
  this 
  particular 
  

   locality, 
  there 
  have 
  been 
  found 
  several 
  other 
  new 
  species 
  of 
  Trilobites, 
  

   the 
  chief 
  of 
  which 
  are 
  briefly 
  described 
  in 
  the 
  pages 
  following. 
  

   * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xv. 
  p. 
  553. 
  

  

  