﻿488 
  PKOCEEDIXGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  tubercles 
  are 
  elevated 
  on 
  pillars, 
  that 
  it 
  is 
  readily 
  distinguished 
  from 
  

   its 
  congeners 
  by 
  this 
  character. 
  One 
  other 
  species, 
  S. 
  Pareti, 
  Ag\, 
  

   has 
  similar 
  deep 
  areolas, 
  but 
  the 
  petaloid 
  areas 
  are 
  relatively 
  nar- 
  

   rower, 
  and 
  the 
  poriferous 
  zones 
  are 
  very 
  nearly 
  as 
  wide 
  as 
  the 
  inter- 
  

   poriferous 
  spaces. 
  

  

  Strati 
  graphical 
  position. 
  — 
  Collected 
  by 
  the 
  Earl 
  of 
  Ducie 
  from 
  the 
  

   calcareous 
  sandstone 
  of 
  bed 
  No. 
  4, 
  where 
  it 
  is 
  not 
  abundant. 
  

  

  Collections. 
  — 
  Earl 
  of 
  Ducie's 
  collection 
  ; 
  my 
  cabinet. 
  

  

  36. 
  Spatangtjs 
  lelphlxus, 
  Defrance. 
  PL 
  XXII. 
  figs. 
  4 
  a, 
  4 
  b. 
  

  

  JSpatangus 
  delphinus, 
  Defrance, 
  Diet. 
  Sc. 
  Nat. 
  1827, 
  torn. 
  1. 
  p. 
  96. 
  

  

  JSpatangus 
  Corsicus, 
  Desor, 
  Cat. 
  Kaisonne, 
  1846, 
  p. 
  113. 
  

  

  Spatangus 
  Desmaresti, 
  Wright, 
  Ann. 
  and 
  Mag. 
  Nat. 
  Hist. 
  1855, 
  

   vol. 
  xv. 
  p. 
  18. 
  

  

  Spatangus 
  delphinus, 
  Desor, 
  Synopsis 
  des 
  Echinides 
  Foss., 
  1858, 
  

   p. 
  421. 
  

  

  Test 
  large, 
  inflated, 
  short, 
  cordate, 
  and 
  carinatcd 
  ; 
  petaloid 
  am- 
  

   bulacra 
  long 
  and 
  narrow, 
  the 
  external 
  poriferous 
  zone 
  of 
  the 
  anterior 
  

   pair 
  much 
  arched, 
  narrow 
  at 
  the 
  upper 
  half, 
  and 
  nearly 
  obsolete 
  at 
  

   the 
  summit 
  ; 
  test 
  much 
  inflated 
  before, 
  with 
  a 
  wide 
  anteal 
  sulcus 
  ; 
  a 
  

   broad 
  ridge 
  extends 
  from 
  the 
  disk 
  to 
  the 
  posterior 
  border, 
  which 
  is 
  

   broadly 
  and 
  sharply 
  truncated 
  ; 
  ambulacral 
  summit 
  very 
  excentral 
  ; 
  

   disk 
  small, 
  with 
  four 
  ovarian 
  holes 
  ; 
  a 
  few 
  large 
  tubercles 
  in 
  rows 
  in 
  

   all 
  the 
  interambulacra, 
  the 
  small 
  tubercles 
  very 
  closely 
  set 
  together 
  ; 
  

   vent 
  large, 
  transversely 
  oval, 
  in 
  the 
  upper 
  part 
  of 
  the 
  truncated 
  

   section 
  ; 
  base 
  plano-convex 
  ; 
  peristome, 
  in 
  the 
  anterior 
  third, 
  large, 
  

   labiate, 
  and 
  transversely 
  oblong. 
  

  

  Diynensions. 
  — 
  Antero- 
  posterior 
  diameter 
  4g- 
  inches 
  ; 
  transverse 
  

   diameter 
  41 
  inches 
  ; 
  height 
  2-J- 
  inches. 
  

  

  Description. 
  — 
  This 
  large 
  Urchin 
  was 
  so 
  imperfectly 
  described 
  by 
  

   Defrance, 
  who 
  gave 
  no 
  figure 
  of] 
  it, 
  that 
  it 
  was 
  long 
  overlooked. 
  Many 
  

   examples 
  resemble 
  so 
  much 
  S. 
  Desmaresti, 
  Goldf., 
  that 
  they 
  were 
  

   considered 
  to 
  be 
  identical 
  with 
  it; 
  under 
  this 
  impression 
  it 
  was 
  

   described 
  by 
  that 
  name 
  in 
  my 
  memoir 
  on 
  the 
  Maltese 
  Echinoderms. 
  

   The 
  test 
  is 
  broader 
  than 
  long, 
  elevated, 
  flattened, 
  and 
  inflated 
  before, 
  

   and 
  broadly 
  truncated 
  behind 
  ; 
  a 
  blunt 
  ridge 
  runs 
  from 
  the 
  disk 
  to 
  the 
  

   posterior 
  border. 
  The 
  petaloid 
  areas 
  forming 
  the 
  ambulacral 
  star 
  are 
  

   long, 
  narrow, 
  and 
  biflexed 
  ; 
  the 
  external 
  poriferous 
  zone 
  of 
  the 
  anterior 
  

   pair 
  is 
  much 
  arched 
  forwards 
  and 
  flexed 
  outwards 
  ; 
  the 
  pores 
  are 
  

   small 
  in 
  the 
  upper 
  half 
  of 
  the 
  zone, 
  and 
  near 
  the 
  summit 
  they 
  form 
  

   a 
  simple 
  row 
  of 
  minute 
  holes. 
  In 
  the 
  external 
  zone 
  of 
  the 
  posterior 
  

   pair 
  the 
  holes 
  are 
  likewise 
  small. 
  The 
  dorsal 
  surface 
  of 
  the 
  interam- 
  

   bulacra 
  between 
  the 
  petaloid 
  areas 
  supports 
  two 
  or 
  three 
  irregular 
  

   rows 
  of 
  larger 
  tubercles, 
  which 
  are 
  proportionately 
  greater 
  in 
  small 
  

   specimens. 
  The 
  other 
  parts 
  of 
  the 
  upper 
  surface 
  are 
  studded 
  with 
  

   small 
  close-set 
  tubercles, 
  and 
  the 
  general 
  surface 
  of 
  the 
  inter- 
  

   tubercular 
  spaces 
  is 
  covered 
  with 
  a 
  fine 
  granulation. 
  The 
  anterior 
  

   border 
  is 
  very 
  flat, 
  the 
  anteal 
  sulcus 
  broad 
  and 
  deep, 
  and 
  the 
  pores 
  

   of 
  the 
  ambulacrum 
  invisible. 
  Behind 
  the 
  small 
  apical 
  disk, 
  with 
  its 
  

   four 
  ovarian 
  holes, 
  a 
  blunt 
  arched 
  ridge 
  extends 
  to 
  the 
  posterior 
  border, 
  

  

  