﻿Geological 
  Society. 
  867 
  

  

  fore 
  to 
  be 
  placed 
  with 
  the 
  Eugeniaerinidae, 
  although 
  its 
  characters 
  

   arc 
  not 
  those 
  of 
  the 
  family 
  as 
  heretofore 
  defined. 
  This 
  is 
  seen 
  

   from 
  the 
  following 
  diagnosis 
  : 
  — 
  

  

  Trigonocrinus, 
  gen. 
  nov. 
  — 
  Calyx 
  roughly 
  triangular 
  or 
  trilobate 
  

   in 
  section. 
  Basals 
  4, 
  but 
  one 
  so 
  atrophied 
  as 
  to 
  be 
  almost 
  invisible 
  ; 
  

   all 
  fused 
  into 
  a 
  basal 
  ring. 
  First 
  radials 
  4 
  ; 
  the 
  two 
  on 
  either 
  side 
  

   of 
  the 
  smallest 
  basal 
  half 
  the 
  size 
  of 
  the 
  others, 
  thus 
  maintaining 
  

   the 
  triangular 
  symmetry 
  ; 
  all 
  closely 
  united, 
  with 
  each 
  suture-line 
  

   in 
  a 
  groove. 
  Processes 
  of 
  radials 
  well 
  developed, 
  forming 
  spines 
  

   homologous 
  with 
  the 
  petals 
  of 
  Phyllocrinus 
  ; 
  except 
  the 
  adjacent 
  

   processes 
  of 
  tho 
  smaller 
  radials, 
  which 
  only 
  form 
  a 
  minute 
  ridge. 
  

   Articular 
  surface 
  of 
  radials 
  curved 
  gently 
  inwards 
  and 
  upwards 
  ; 
  

   muscular 
  impressions 
  indistinct 
  or 
  absent: 
  no 
  articular 
  ridge 
  ; 
  no 
  

   canal-aperture. 
  Arms 
  unknown 
  : 
  ? 
  represented 
  by 
  fleshy 
  appen- 
  

   dages. 
  Calycal 
  cavity 
  contained 
  in 
  first 
  radials 
  ; 
  with 
  small 
  round 
  

   ventral 
  aperture, 
  surrounded 
  by 
  a 
  rim, 
  which 
  is 
  the 
  only 
  relic 
  of 
  a 
  

   muscular 
  attachment. 
  Stem 
  unknown. 
  

  

  The 
  two 
  calyces 
  belong 
  to 
  the 
  same 
  species, 
  viz. 
  T. 
  Uratus,sp. 
  nov. 
  

   — 
  Calyx 
  rather 
  more 
  elongate 
  than 
  in 
  the 
  known 
  species 
  of 
  Phyllo- 
  

   crinus 
  ; 
  basals 
  ornamented 
  with 
  minute 
  granules 
  ; 
  radials 
  ornamented 
  

   with 
  similar 
  granules 
  run 
  into 
  curved 
  ridges, 
  which, 
  owing 
  to 
  their 
  

   differing 
  intensity, 
  give 
  an 
  imbricated 
  appearance; 
  spines 
  triangular 
  

   in 
  section, 
  with 
  the 
  base 
  of 
  the 
  triangle 
  directed 
  inwards, 
  the 
  apex 
  

   outwards, 
  the 
  angles 
  often 
  rounded. 
  

  

  The 
  differentiation 
  of 
  Trigonocrinus 
  from 
  the 
  central 
  Eugenia- 
  

   crinid 
  type 
  has 
  been 
  effected 
  on 
  the 
  one 
  hand 
  in 
  accordance 
  with 
  

   the 
  principles 
  of 
  ''Degeneration," 
  "Reversion," 
  and 
  " 
  Use 
  and 
  Dis- 
  

   use 
  " 
  ; 
  while, 
  on 
  the 
  other 
  hand, 
  it 
  exemplifies 
  certain 
  methods 
  of 
  

   change 
  in 
  organic 
  forms, 
  which 
  may 
  be 
  referred 
  to 
  the 
  categories 
  

   of 
  (1) 
  Sport, 
  (2) 
  Hypertrophy 
  and 
  Atrophy, 
  ('■>) 
  Fusion 
  and 
  Fission. 
  

   Thus 
  considered 
  it 
  is 
  of 
  unique 
  interest 
  among 
  Crinoidea.' 
  An 
  ex- 
  

   amination 
  of 
  the 
  variations 
  in 
  symmetry 
  presented 
  by 
  the 
  Echino- 
  

   dermata 
  suggests 
  the 
  conclusion 
  that 
  the 
  I'entamerous 
  type 
  was 
  

   originally 
  evolved 
  from 
  another 
  system, 
  or 
  at 
  least 
  that 
  it 
  was 
  

   selected 
  from 
  among 
  other 
  variations, 
  that 
  it 
  has 
  survived, 
  and 
  that 
  

   it 
  has 
  been 
  kept 
  true, 
  as 
  being 
  the 
  fittest. 
  

  

  Appendix 
  I. 
  Sudden 
  deviations 
  from 
  normal 
  symmetry 
  in 
  Neo- 
  

   ciinoidea. 
  

  

  A 
  collection 
  of 
  instances 
  from 
  previous 
  authors, 
  with 
  a 
  few 
  addi- 
  

   tions, 
  the 
  whole 
  illustrating 
  the 
  latter 
  portion 
  of 
  the 
  paper. 
  

  

  Appendix 
  II. 
  On 
  Marsupites 
  testudinarius, 
  von 
  Schlotheim, 
  sp. 
  

  

  A 
  synonymy 
  of 
  t 
  lie 
  genus 
  Marsupites 
  : 
  it 
  contains 
  but 
  one 
  known 
  

   species, 
  and 
  all 
  other 
  names 
  must 
  yield 
  to 
  this 
  one. 
  

  

  2. 
  "On 
  Archceocyaihus, 
  Billings, 
  and 
  on 
  other 
  Genera 
  allied 
  

   thereto 
  or 
  associated 
  therewith 
  from 
  the 
  Cambrian 
  Strata 
  of 
  North 
  

   America. 
  Spain, 
  Sardinia, 
  and 
  Scotland.*' 
  By 
  Dr. 
  C 
  J. 
  Hinde, 
  

   F.G.S. 
  

  

  A 
  revision 
  of 
  the 
  type 
  specimens 
  of 
  the 
  three 
  species 
  included 
  by 
  

   Mr. 
  Billings 
  in 
  the 
  genus 
  Archfeocyathus 
  shows 
  that 
  each 
  of 
  the 
  

  

  