﻿482 
  PROCEEDINGS 
  OP 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  marginal. 
  The 
  peristome 
  lies 
  in 
  a 
  depression 
  opposite 
  the 
  disk, 
  but 
  

   is 
  unfortunately 
  concealed 
  by 
  hard 
  matrix. 
  

  

  Affinities 
  and 
  differences. 
  — 
  The 
  oblong 
  form, 
  tumid 
  sides, 
  and 
  

   shorter 
  ambulacra 
  distinguish 
  this 
  species 
  from 
  E. 
  hemisplicericus. 
  

   The 
  convexity 
  of 
  the 
  base, 
  and 
  equality 
  in 
  the 
  width 
  of 
  the 
  ambu- 
  

   lacra, 
  afford 
  likewise 
  good 
  characters 
  by 
  which 
  these 
  two 
  allied 
  species 
  

   may 
  be 
  distinguished 
  from 
  each 
  other. 
  

  

  StratigrapTncal 
  position. 
  — 
  (" 
  This 
  species 
  is 
  not 
  at 
  all 
  uncommon 
  

   in 
  bed 
  No. 
  5, 
  but, 
  from 
  the 
  hardness 
  of 
  the 
  rock, 
  is 
  by 
  no 
  means 
  easily 
  

   extracted. 
  I 
  have 
  often 
  seen 
  it, 
  associated 
  with 
  Scutella 
  subrotunda." 
  

   A. 
  L. 
  A.) 
  It 
  is 
  found 
  in 
  the 
  Molasse 
  (Miocene) 
  of 
  several 
  departments 
  

   in 
  France, 
  and 
  in 
  the 
  Canton 
  of 
  Neufchatel, 
  Switzerland. 
  

  

  Collections. 
  — 
  Museum 
  of 
  the 
  Geological 
  Society 
  ; 
  my 
  cabinet. 
  

  

  Genus 
  Amblypygus, 
  Agassiz, 
  1840. 
  

  

  Urchins 
  in 
  general 
  large, 
  with 
  a 
  depressed 
  ovoid 
  test 
  and 
  a 
  

   rounded 
  border 
  ; 
  ambulacral 
  areas 
  unequal 
  in 
  width 
  and 
  length 
  ; 
  

   poriferous 
  zones 
  very 
  narrow, 
  extending 
  from 
  the 
  disk 
  to 
  the 
  peri- 
  

   stome 
  ; 
  base 
  concave 
  and 
  arched 
  ; 
  mouth-opening 
  near 
  the 
  middle 
  ; 
  

   peristome 
  oblique, 
  angular, 
  without 
  any 
  poriferous 
  petals. 
  Vent 
  

   large, 
  pyriform, 
  situated 
  at 
  the 
  base, 
  between 
  the 
  mouth 
  and 
  the 
  

   border. 
  Apical 
  disk 
  small, 
  nearly 
  central, 
  with 
  four 
  ovarian 
  pores. 
  

  

  This 
  genus 
  resembles 
  Pygaulus 
  in 
  the 
  general 
  form 
  of 
  the 
  test, 
  

   but 
  is 
  distinguished 
  by 
  the 
  position 
  of 
  the 
  vent, 
  which 
  always 
  occu- 
  

   pies 
  the 
  base 
  between 
  the 
  peristome 
  and 
  the 
  border 
  ; 
  the 
  poriferous 
  

   zones 
  are 
  simple 
  throughout, 
  and 
  are 
  not 
  petaloid 
  around 
  the 
  peri- 
  

   stome. 
  The 
  narrowness 
  of 
  the 
  poriferous 
  zones 
  and 
  the 
  absence 
  of 
  

   oral 
  lobes 
  and 
  petals 
  serve 
  to 
  distinguish 
  Amblypygus 
  from 
  Conocly- 
  

   pus. 
  All 
  the 
  species 
  are 
  extinct, 
  and 
  found 
  in 
  the 
  Tertiary 
  rocks. 
  

  

  18. 
  Amblypygus 
  Melitensis, 
  Wright, 
  sp. 
  nov. 
  PI. 
  XXI. 
  figs. 
  3a 
  — 
  3c. 
  

  

  Test 
  elongated, 
  depressed, 
  border 
  inflated 
  ; 
  ambulacral 
  areas 
  nar- 
  

   row, 
  unequal 
  in 
  width, 
  the 
  single 
  ambulacrum 
  narrowest 
  ; 
  pori- 
  

   ferous 
  zones 
  very 
  narrow 
  ; 
  pores 
  a 
  little 
  more 
  apart 
  on 
  the 
  upper 
  

   surface 
  than 
  at 
  the 
  border 
  ; 
  base 
  concave, 
  arched 
  in 
  the 
  antero- 
  

   posterior 
  direction 
  ; 
  mouth- 
  opening 
  nearly 
  central, 
  oblique, 
  and 
  an- 
  

   gular 
  ; 
  vent 
  oblong, 
  occupying 
  the 
  space 
  between 
  the 
  peristome 
  and 
  

   the 
  border. 
  

  

  Dimensions. 
  — 
  Length 
  1| 
  inch 
  ; 
  breadth 
  14- 
  inch 
  ; 
  height 
  ^ 
  inch. 
  

  

  Description. 
  — 
  This 
  beautiful 
  little 
  Urchin 
  might 
  be 
  mistaken 
  for 
  a 
  

   Pygaulus, 
  if 
  the 
  position 
  of 
  the 
  vent 
  were 
  overlooked 
  ; 
  it 
  has 
  a 
  regu- 
  

   lar 
  ovoid 
  form, 
  convex 
  and 
  depressed 
  above, 
  concave 
  and 
  arched 
  

   below 
  ; 
  the 
  ambulacral 
  areas 
  are 
  narrowly 
  lanceolate 
  and 
  of 
  un- 
  

   equal 
  width, 
  the 
  ambulacrum 
  being 
  the 
  smallest, 
  and 
  the 
  anterior 
  

   pair 
  the 
  widest. 
  The 
  poriferous 
  zones 
  are 
  very 
  narrow, 
  and 
  the 
  

   pores 
  appear 
  to 
  be 
  a 
  shade 
  more 
  apart 
  on 
  the 
  upper 
  surface 
  than 
  

   they 
  are 
  at 
  the 
  border 
  or 
  base. 
  The 
  interambulacra 
  are 
  likewise 
  

   unequal 
  in 
  width, 
  the 
  sides 
  are 
  tumid, 
  and 
  the 
  border 
  is 
  rounded. 
  

   The 
  base 
  is 
  convex 
  at 
  the 
  sides, 
  and 
  concave 
  towards 
  the 
  centre, 
  

   where 
  the 
  two 
  openings 
  of 
  the 
  test 
  are 
  situated 
  ; 
  it 
  is 
  likewise 
  

  

  