﻿LITTLE-KNOWN 
  JTJBASSIC 
  CKLNOIDS. 
  

  

  41 
  

  

  axillaries 
  of 
  the 
  two 
  species 
  also 
  differ 
  in 
  their 
  relative 
  proportions 
  ; 
  

   and 
  the 
  same 
  is 
  the 
  case 
  with 
  the 
  first 
  brachials, 
  those 
  of 
  Ant. 
  

   latiradia 
  being 
  the 
  more 
  wedge-shaped. 
  Both 
  species, 
  like 
  most 
  of 
  

   the 
  Jurassic 
  Antedons, 
  belong 
  to 
  a 
  section 
  of 
  the 
  genus 
  which 
  is 
  less 
  

   sharply 
  distinguished 
  from 
  Actinometra 
  than 
  the 
  great 
  majority 
  of 
  

   recent 
  species 
  are. 
  In 
  most 
  recent 
  Antedons, 
  especially 
  in 
  those 
  

   which 
  resemble 
  these 
  two 
  species 
  in 
  having 
  only 
  ten 
  arms, 
  the 
  axillaries 
  

   are 
  nearly 
  as 
  long 
  as, 
  or 
  sometimes 
  even 
  longer 
  than, 
  wide, 
  and 
  have 
  

   more 
  or 
  less 
  marked 
  backward 
  projections 
  into 
  the 
  second 
  radials. 
  

   This 
  last 
  feature 
  is 
  visible 
  even 
  in 
  Ant. 
  macrocnema 
  of 
  Sydney 
  

   Harbour, 
  which 
  is 
  remarkable 
  for 
  presenting 
  many 
  of 
  the 
  peculia- 
  

   rities 
  of 
  Jurassic 
  Antedons. 
  It 
  likewise 
  approaches 
  Actinometra 
  in 
  

   the 
  relative 
  width 
  of 
  the 
  axillaries, 
  and 
  also 
  of 
  the 
  articular 
  faces 
  of 
  

   the 
  first 
  radials. 
  In 
  most 
  recent 
  Comatulce, 
  including 
  some 
  species 
  

   of 
  Antedon 
  and 
  all 
  Actinometrce, 
  the 
  width 
  of 
  the 
  articular 
  faces 
  of 
  

   the 
  first 
  radials 
  exceeds 
  their 
  height, 
  though 
  in 
  some 
  Antedons 
  these 
  

   faces 
  are 
  higher 
  than 
  they 
  are 
  wide 
  ; 
  but 
  the 
  relative 
  proportions 
  

   of 
  the 
  two 
  diameters 
  vary 
  considerably, 
  the 
  width 
  being 
  greatest 
  in 
  

   the 
  Actinometrce. 
  The 
  same 
  is 
  the 
  case 
  with 
  the 
  dimensions 
  of 
  the 
  

   radial 
  axillaries, 
  as 
  may 
  be 
  seen 
  from 
  the 
  subjoined 
  Table 
  :— 
  

  

  Species. 
  

  

  Articular 
  faces 
  of 
  

   first 
  Radials. 
  

   Proportion 
  of 
  

  

  width 
  to 
  height. 
  

  

  Eadial 
  Axillaries. 
  

   Proportion 
  of 
  

   width 
  to 
  length. 
  

  

  Recent. 
  

   Antedon 
  Eschrichtii 
  

  

  11:10 
  

   6: 
  5 
  

  

  16: 
  9 
  

   7: 
  5 
  

  

  17:16 
  

  

  16:15 
  

   8: 
  5 
  

  

  2: 
  1 
  

   5: 
  2 
  

  

  20:11 
  

   17:10 
  

  

  

  Actinometra 
  strata 
  , 
  

  

  Jukesii 
  

  

  Fossil. 
  

   Antedon 
  latiradia 
  

  

  calloviensis 
  , 
  

  

  

  

  In 
  this 
  last 
  respect 
  the 
  two 
  fossil 
  species 
  under 
  consideration 
  ap- 
  

   proach 
  the 
  type 
  of 
  Actinometra 
  rather 
  than 
  that 
  of 
  most 
  Antedons, 
  

   though 
  the 
  axillaries 
  of 
  Ant. 
  calloviensis 
  are 
  but 
  little 
  wider 
  

   than 
  those 
  of 
  Ant. 
  macrocnema 
  and 
  other 
  somewhat 
  aberrant 
  

   species. 
  The 
  articular 
  faces 
  of 
  the 
  first 
  radials 
  are 
  not 
  exposed 
  in 
  

   Ant. 
  calloviensis 
  ; 
  and, 
  in 
  default 
  of 
  better 
  evidence, 
  I 
  was 
  at 
  first 
  

   led 
  to 
  refer 
  this 
  species 
  to 
  Actinometra*, 
  chiefly 
  on 
  account 
  of 
  its 
  

   comparatively 
  small 
  centrodorsal 
  and 
  the 
  width 
  of 
  its 
  second 
  and 
  

   third 
  radials. 
  This 
  took 
  place 
  before 
  the 
  discovery 
  of 
  Ant. 
  latiradia, 
  

   to 
  which 
  the 
  Kelloway 
  Comatida 
  is 
  evidently 
  very 
  closely 
  allied. 
  

   The 
  older 
  species 
  has 
  relatively 
  wider 
  axillaries 
  than 
  Ant. 
  cal- 
  

  

  * 
  Abstracts 
  of 
  the 
  Proc. 
  Geol. 
  Soc. 
  no. 
  407, 
  p. 
  98. 
  

  

  