﻿^°^ 
  53*1 
  AFFINITIES 
  OF 
  THE 
  ECHINOTHUELDiE. 
  119 
  

  

  condition 
  are 
  not 
  common 
  in 
  Peclina 
  ; 
  but 
  they 
  do 
  occur, 
  and 
  they 
  

   are 
  identical 
  in 
  arrangement 
  with 
  the 
  ambulacral 
  plates 
  near 
  the 
  

   apex 
  of 
  Pelanecliinus 
  and 
  Phormosoma. 
  

  

  Thus 
  Peclina 
  suggests 
  the 
  point 
  at 
  which 
  the 
  ecbinothurid 
  branch 
  

   diverged 
  from 
  the 
  main 
  diademoid 
  stem. 
  The 
  gap 
  between 
  Pelan- 
  

   ecliinus 
  and 
  the 
  nearest 
  member 
  of 
  the 
  rest 
  of 
  the 
  order 
  Diademoida 
  

   is 
  bridged 
  by 
  a 
  new 
  echinid 
  from 
  the 
  German 
  Jura, 
  which 
  I 
  have 
  

   accordingly 
  named 
  Peclinotlmria. 
  Its 
  test 
  being 
  small 
  and 
  rigid, 
  it 
  

   appears 
  to 
  be 
  nearer 
  to 
  the 
  Pedinidse 
  than 
  to 
  the 
  Echinothuridse. 
  

  

  Pedixothtjeia, 
  gen. 
  nov. 
  

  

  Diagnosis. 
  — 
  Pedinidae 
  with 
  the 
  test 
  small, 
  rigid, 
  and 
  turban- 
  

   shaped. 
  

  

  Apical 
  system 
  large, 
  its 
  diameter 
  about 
  half 
  that 
  of 
  the 
  test. 
  

   The 
  arrangement 
  of 
  the 
  plates 
  is 
  unknown. 
  

  

  Ambulacra. 
  — 
  Near 
  the 
  apex 
  the 
  plates 
  are 
  simple 
  primaries. 
  

   At 
  the 
  ambitus 
  the 
  pore-pairs 
  are 
  biserial, 
  owing 
  to 
  the 
  reduction 
  

   of 
  alternate 
  primaries 
  to 
  demi-plates. 
  Below 
  the 
  ambitus 
  the 
  pore- 
  

   pairs 
  are 
  triserial, 
  owing 
  to 
  the 
  presence 
  of 
  a 
  second 
  demi-plate 
  on 
  

   the 
  horizontal 
  suture 
  between 
  two 
  primaries. 
  

  

  Near 
  the 
  peristome 
  the 
  plates 
  are 
  not 
  compound 
  ; 
  they 
  are 
  all 
  

   demi-plates, 
  and 
  occur 
  in 
  three 
  series. 
  Those 
  of 
  the 
  median 
  series 
  

   are 
  the 
  largest, 
  and 
  they 
  may 
  bear 
  a 
  miliar}' 
  granule. 
  

  

  There 
  are 
  no 
  primary 
  tubercles 
  on 
  the 
  ambulacra 
  ; 
  but 
  two 
  rows 
  

   of 
  small, 
  regular 
  granules 
  run 
  down 
  each 
  ambulacrum. 
  Near 
  the 
  

   peristome 
  they 
  are 
  small, 
  and 
  limited 
  to 
  the 
  primary 
  plate 
  on 
  

   which 
  they 
  occur. 
  

  

  Interambulacra. 
  — 
  The 
  plates 
  are 
  unituberculate. 
  Upon 
  each 
  

   there 
  is 
  a 
  prominent, 
  primary 
  tubercle, 
  which 
  is 
  perforate 
  and 
  

   crenulate. 
  About 
  seven 
  in 
  each 
  vertical 
  series. 
  The 
  mamelons 
  

   are 
  perforated. 
  Near 
  the 
  peristome 
  the 
  ambulacra 
  are 
  broader 
  than 
  

   the 
  interambulacra. 
  

  

  Peristome 
  small 
  ; 
  branchial 
  slits 
  very 
  deep. 
  

  

  Distribution. 
  — 
  Jurassic, 
  Germany. 
  

  

  Pedixothtteia 
  cidakoides, 
  sp. 
  nov. 
  (PI. 
  VII. 
  figs. 
  1-3.) 
  

  

  Diagnosis. 
  — 
  Test 
  circular, 
  depressed. 
  Oral 
  surface 
  very 
  flat; 
  

   aboral 
  half 
  slightly 
  tumid. 
  

  

  Apical 
  system 
  slightly 
  more 
  than 
  half 
  the 
  width 
  of 
  the 
  test 
  

   in 
  diameter. 
  

  

  Interambulac 
  r 
  a. 
  — 
  Seven 
  plates 
  in 
  each 
  vertical 
  series. 
  Scrobi- 
  

   cular 
  areas 
  confluent. 
  Miliary 
  granules 
  scarce. 
  

  

  Ambulacra. 
  — 
  Structure 
  as 
  in 
  generic 
  diagnosis. 
  The 
  change 
  

   from 
  the 
  uniserial 
  to 
  the 
  biserial 
  arrangement 
  of 
  the 
  pore-pairs 
  

   occurs 
  at 
  the 
  12th 
  or 
  13th 
  plate 
  from 
  the 
  apex. 
  

  

  Dimensions. 
  — 
  Diameter, 
  12 
  millim. 
  ; 
  height, 
  5 
  millim. 
  ; 
  diameter 
  

   of 
  apical 
  area, 
  7 
  millim. 
  ; 
  diameter 
  of 
  peristome, 
  4 
  millim. 
  ; 
  width 
  

   of 
  ambulacrum 
  at 
  ambitus, 
  2| 
  millim. 
  ; 
  width 
  of 
  interambulacrum 
  

  

  