﻿WEIGHT 
  AND 
  ADAMS 
  MALTESE 
  ECHINODERMS. 
  485 
  

  

  Collections. 
  — 
  Royal 
  School 
  of 
  Mines 
  ; 
  British 
  Museum 
  ; 
  Bristol 
  Mu- 
  

   seum 
  ; 
  Museum 
  of 
  the 
  Geological 
  Society 
  ; 
  Earl 
  of 
  Ducie's 
  cabinet. 
  

  

  26. 
  Schizaster 
  Desori, 
  "Wright. 
  

  

  Stratigrapliical 
  position. 
  — 
  " 
  All 
  my 
  specimens 
  are 
  from 
  No. 
  4 
  bed, 
  

   where 
  this 
  Urchin 
  is 
  not 
  uncommon, 
  and 
  is 
  usually 
  associated 
  with 
  

   Hemiaster 
  Scillce, 
  H. 
  Cotteaui, 
  and 
  Brissopsis 
  Grateloupi, 
  also 
  Schi- 
  

   zaster 
  Parkinsonii 
  and 
  Prenaster 
  excentricus." 
  (A. 
  L. 
  A.) 
  

  

  Collections. 
  — 
  Common 
  in 
  all 
  collections 
  of 
  Maltese 
  Urchins. 
  

  

  Genus 
  Brisstts, 
  Aristotle, 
  Klein. 
  

  

  Large 
  Urchins 
  with 
  an 
  ovoid 
  or 
  elongated 
  test 
  ; 
  ambulacral 
  sum- 
  

   mit 
  very 
  excentral, 
  and 
  ambulacrum 
  rudimentary 
  ; 
  anterior 
  pair 
  of 
  

   ambulacra 
  deeply 
  sunk 
  and 
  nearly 
  transverse 
  ; 
  posterior 
  pair 
  forming 
  

   an 
  acute 
  angle 
  with 
  the 
  anterior 
  pair 
  and 
  directed 
  backwards, 
  they 
  

   are 
  sinuous 
  and 
  concave; 
  the 
  peripetalous 
  fasciole 
  closely 
  embraces 
  the 
  

   ambulacral 
  pairs, 
  and 
  forms 
  an 
  arch 
  on 
  the 
  anterior 
  border 
  ; 
  the 
  

   subanal 
  fasciole 
  describes 
  a 
  cordate 
  figure 
  below 
  the 
  vent, 
  which 
  is 
  

   large, 
  oblong, 
  and 
  vertical. 
  Apical 
  disk 
  small, 
  four 
  genital 
  pores. 
  

   Madreporiform 
  body 
  elongated 
  between 
  the 
  plates. 
  Mouth 
  near 
  the 
  

   anterior 
  border; 
  peristome 
  labiate 
  on 
  the 
  posterior 
  border. 
  This 
  

   genus 
  comprises 
  living 
  and 
  fossil 
  species 
  ; 
  the 
  latter 
  are 
  found 
  only 
  in 
  

   the 
  Tertiary 
  formations, 
  and 
  are 
  chiefly 
  of 
  Miocene 
  and 
  Pliocene 
  age. 
  

  

  27. 
  Brisstts 
  latus, 
  "Wright. 
  

  

  Distinctive 
  characters. 
  — 
  The 
  breadth 
  of 
  the 
  test; 
  the 
  depression 
  

   of 
  the 
  upper 
  surface 
  ; 
  the 
  depth 
  of 
  the 
  ambulacra, 
  the 
  anterior 
  pair 
  

   being 
  less 
  transverse, 
  and 
  the 
  posterior 
  pair 
  more 
  expanded 
  than 
  in 
  

   the 
  other 
  species 
  ; 
  the 
  ambulacral 
  summit 
  is 
  more 
  central, 
  and 
  the 
  

   anteal 
  sulcus 
  deeper 
  than 
  in 
  its 
  congeners. 
  

  

  Stratigrapliical 
  position. 
  — 
  I 
  have 
  only 
  found 
  this 
  Urchin 
  in 
  No. 
  1, 
  

   and 
  chiefly 
  in 
  the 
  lower 
  or 
  coralline 
  stratum, 
  where 
  in 
  certain 
  

   localities 
  it 
  is 
  not 
  uncommon, 
  and 
  usually 
  met 
  with 
  in 
  a 
  frag- 
  

   mentary 
  condition. 
  Several 
  good 
  specimens 
  have 
  been 
  found 
  in 
  the 
  

   above 
  stratum 
  at 
  the 
  fault 
  in 
  Eorn-i-riale 
  Bay, 
  where 
  the 
  accom- 
  

   panying 
  specimens 
  were 
  discovered. 
  What 
  appear 
  to 
  be 
  the 
  spines 
  

   of 
  this 
  Urchin 
  are 
  seen 
  on 
  the 
  under 
  surface 
  of 
  the 
  broadest 
  of 
  the 
  

   specimens. 
  

  

  Collections. 
  — 
  Museum 
  of 
  the 
  Royal 
  School 
  of 
  Mines; 
  Earl 
  of 
  

   Ducie's 
  cabinet 
  ; 
  Museum 
  of 
  the 
  Geological 
  Society 
  ; 
  and 
  my 
  cabinet. 
  

  

  28. 
  Brisstts 
  cylindrictts, 
  Agassiz. 
  

  

  Stratigrapliical 
  position. 
  — 
  " 
  Allowing 
  for 
  the 
  effects 
  of 
  pressure, 
  

   there 
  is 
  evidently 
  some 
  diversity 
  in 
  the 
  configuration 
  of 
  the 
  speci- 
  

   mens, 
  chiefly 
  in 
  the 
  dorsal 
  surfaces, 
  which 
  appear 
  flatter 
  in 
  some 
  

   than 
  in 
  others. 
  This 
  Urchin 
  is 
  common 
  in 
  the 
  coralline 
  stratum 
  of 
  

   No. 
  1, 
  especially 
  on 
  certain 
  cliff-exposures 
  on 
  the 
  south 
  coast. 
  It 
  

   is 
  often 
  associated 
  with 
  Brissus 
  imbricatus 
  (so 
  named 
  and 
  sent). 
  

   There 
  does 
  not 
  appear 
  to 
  be 
  any 
  difference 
  between 
  the 
  specimens 
  

   from 
  Nos. 
  1 
  and 
  5 
  in 
  the 
  collection. 
  

  

  