﻿Palaeozoic 
  B 
  waived 
  Entomostraca. 
  381 
  

  

  gin 
  and 
  a 
  very 
  shallow 
  valley 
  more 
  forward. 
  This 
  is 
  a 
  very 
  

   weak 
  Beyrichian 
  form. 
  

  

  Fig. 
  9 
  (also 
  from 
  no. 
  28) 
  presents 
  a 
  large 
  hinder 
  (gigot) 
  

   lobe, 
  an 
  ovate, 
  isolated, 
  middle 
  lobe, 
  and 
  a 
  divided 
  anterior 
  

   lobe, 
  the 
  upper 
  portion 
  of 
  which 
  is 
  feeble, 
  but 
  the 
  lower 
  part 
  

   is 
  swollen, 
  being 
  hypertrophied, 
  as 
  is 
  usual 
  with 
  many 
  Bey- 
  

   richice 
  (see 
  Ann. 
  & 
  Mag. 
  Nat. 
  Hist. 
  ser. 
  5, 
  vol. 
  xvii. 
  1886, 
  

   pp. 
  339-343). 
  Another 
  such 
  individual 
  is 
  present 
  in 
  speci- 
  

   men 
  no. 
  24 
  associated 
  with 
  Orthonota 
  and 
  Gucullella 
  *? 
  

  

  The 
  absence 
  of 
  real 
  differences 
  (of 
  essential 
  value) 
  in 
  the 
  

   series 
  of 
  six 
  Beyrichian 
  forms 
  described 
  above 
  allows 
  of 
  their 
  

   being 
  referred 
  to 
  B. 
  Klcedeni 
  as 
  so 
  many 
  subvarietal 
  indi- 
  

   viduals 
  falling 
  into 
  one 
  varietal 
  group. 
  Not 
  one 
  of 
  them 
  is 
  

   exactly 
  the 
  same 
  as 
  the 
  type 
  of 
  the 
  species, 
  nor 
  do 
  they 
  take 
  

   on 
  what 
  are 
  regarded 
  as 
  the 
  essential 
  characters 
  of 
  any 
  other 
  

   species 
  as 
  at 
  present 
  known. 
  

  

  6. 
  Beyrichia 
  arcuata 
  (Bean). 
  

   (PI. 
  XVI 
  L. 
  tigs, 
  la, 
  lb, 
  7 
  c.) 
  

  

  Beyrichia 
  arcuata, 
  Jones 
  and 
  Kirk 
  by, 
  Geol. 
  Mag. 
  October 
  188G, 
  p. 
  438, 
  

   pi. 
  xii. 
  figs. 
  12-14. 
  

  

  Fig. 
  7 
  (from 
  specimen 
  no. 
  32) 
  has 
  a 
  short, 
  curved, 
  anterior* 
  

   furrow, 
  and 
  a 
  deep, 
  straight, 
  median 
  sulcus, 
  with 
  a 
  distinct, 
  

   though 
  slight, 
  lobe 
  between 
  them. 
  

  

  The 
  geological 
  persistency 
  of 
  this 
  form 
  (fig. 
  7) 
  is 
  shown 
  by 
  

   the 
  similarity 
  of 
  some 
  Carboniferous 
  Ostracoda 
  to 
  our 
  figure. 
  

   Beyrichiopsis 
  simplex, 
  J. 
  & 
  K. 
  (Geol. 
  Mag. 
  dec. 
  3, 
  vol. 
  iii. 
  

   p. 
  437, 
  pi. 
  xii. 
  fig. 
  4), 
  is 
  near 
  to 
  it, 
  but 
  has 
  a 
  shorter 
  median 
  

   and 
  weaker 
  anterior 
  sulcus. 
  Beyrichia 
  cratigera, 
  Brady 
  

   {ibid. 
  fig. 
  7), 
  approaches 
  it, 
  and 
  B. 
  arcuata 
  (Bean) 
  {ibid. 
  

   fig. 
  13) 
  still 
  more 
  nearly. 
  Their 
  passage 
  into 
  the 
  common 
  

   three-lobed 
  Beyrichice 
  is 
  illustrated 
  by 
  figs. 
  8-10, 
  ibid., 
  also 
  

   by 
  some 
  figures 
  in 
  pi. 
  viii. 
  Ann. 
  & 
  Mag. 
  Nat. 
  Hist. 
  ser. 
  5, 
  

   vol. 
  xviii. 
  1886. 
  

  

  This 
  Upper-Silurian 
  Ostracode, 
  then, 
  is 
  a 
  Beyrichia 
  different 
  

   from 
  those 
  of 
  the 
  B. 
  Kloedeni 
  type, 
  and 
  plentiful 
  enough 
  

   afterwards 
  in 
  Carboniferous 
  times, 
  when 
  the 
  representatives 
  

   of 
  the 
  latter 
  were 
  rare, 
  though 
  of 
  large 
  size 
  {B. 
  gigantea). 
  

  

  In 
  the 
  Coal-measures 
  B. 
  arcuata 
  is 
  usually 
  accompanied 
  

   by 
  plant-remains, 
  together 
  with 
  Anthracosiw 
  and 
  such-like 
  

   shells 
  and 
  other 
  fossils 
  not 
  of 
  decidedly 
  marine 
  types 
  ; 
  in 
  the 
  

   Gannister-coal 
  series, 
  however, 
  it 
  occurs 
  with 
  Goniatites, 
  

   and 
  Mr. 
  Kirkby 
  believes 
  that 
  B. 
  arcuata 
  is 
  not 
  truly 
  a 
  fresh- 
  

  

  * 
  Judging 
  from 
  its 
  position 
  in 
  analogous 
  species. 
  

  

  