﻿THE 
  

  

  155 
  

  

  number 
  of 
  four-rayed 
  individuals 
  is 
  extremely 
  small. 
  Although 
  

   such 
  a 
  specimen 
  would 
  assuredly 
  be 
  preserved 
  by 
  every 
  one 
  that 
  

   noticed 
  it, 
  yet 
  there 
  is 
  among 
  the 
  many 
  hundred 
  calyces 
  of 
  Eugenia- 
  

   crinus 
  at 
  the 
  British 
  Museum 
  only 
  one 
  such 
  form, 
  and 
  in 
  all 
  the 
  

   collections 
  I 
  examined 
  on 
  the 
  continent 
  I 
  succeeded 
  in 
  finding 
  two 
  

   at 
  most 
  ; 
  one 
  of 
  these 
  is 
  a 
  Eug. 
  nutans, 
  at 
  Tiibingen, 
  and 
  is 
  figured 
  

   in 
  Quenstedt's 
  Atlas 
  to 
  the 
  ' 
  Petrefactenkunde 
  Deutschlands,' 
  Taf. 
  cv. 
  

   figs. 
  179-181 
  ; 
  the 
  other 
  is 
  a 
  Eug. 
  caryophyllatus, 
  at 
  Stuttgart. 
  

   Rosinus 
  figures 
  a 
  four-rayed 
  Eug. 
  caryophyllatus 
  under 
  the 
  name 
  

   " 
  Corpus 
  stellare 
  tetragonum 
  et 
  tetractinobolon 
  " 
  *. 
  A. 
  Goldfuss 
  

   figures 
  a 
  four-rayed 
  Eug. 
  caryophyllatus 
  and 
  Eug. 
  nutans 
  f 
  ; 
  other 
  

   writers, 
  such 
  as 
  L. 
  Agassiz 
  %, 
  have 
  alluded 
  to 
  the 
  fact 
  ; 
  but 
  the 
  fore- 
  

   going 
  are 
  all 
  the 
  instances 
  I 
  can 
  find. 
  Further, 
  in 
  those 
  abnormal 
  

   forms 
  and 
  in 
  Tetracrinus 
  the 
  radials 
  are 
  quite 
  regular 
  and 
  equal 
  in 
  

   size 
  ; 
  but 
  in 
  the 
  present 
  genus 
  two 
  of 
  the 
  radials 
  are 
  much 
  smaller 
  

   than 
  the 
  other 
  two, 
  and 
  show 
  a 
  very 
  strong 
  tendency 
  to 
  fusion; 
  

   this 
  is 
  accompanied 
  by 
  a 
  corresponding 
  atrophy 
  of 
  the 
  basal 
  in 
  their 
  

   interradius, 
  and 
  of 
  the 
  processes 
  that 
  would 
  otherwise 
  have 
  formed 
  

   a 
  spine. 
  Consequently, 
  to 
  apply 
  the 
  language 
  of 
  Rosinus, 
  we 
  have 
  

   a 
  body 
  that 
  is 
  morphologically 
  " 
  tetractinobolon," 
  but 
  actually 
  " 
  tri- 
  

   gonum." 
  This 
  character, 
  strongly 
  emphasized 
  by 
  the 
  three 
  spines 
  

   and 
  the 
  three 
  basals, 
  causes 
  me 
  to 
  suggest 
  for 
  the 
  genus 
  the 
  name 
  

   Trigonocrinus. 
  

  

  It 
  is 
  unnecessary 
  to 
  point 
  out 
  that 
  Trigonocrinus 
  cannot 
  be 
  a 
  

   species, 
  or 
  even 
  a 
  close 
  ally, 
  of 
  Tetracrinus, 
  for 
  the 
  latter 
  genus 
  has 
  

   no 
  radial 
  processes. 
  The 
  peculiar 
  character 
  of 
  the 
  processes 
  in 
  Tri- 
  

   gonocrinus, 
  forming 
  what 
  I 
  have 
  called 
  the 
  " 
  spines," 
  allies 
  this 
  

   genus 
  more 
  closely 
  to 
  Phyllocrinus 
  than 
  to 
  any 
  other 
  Eugeniacrinid. 
  

   In 
  Phyllocrinus 
  the 
  processes 
  of 
  two 
  contiguous 
  radials 
  unite 
  to 
  

   form 
  a 
  sort 
  of 
  " 
  petal," 
  whence 
  the 
  generic 
  name. 
  The 
  five 
  petals, 
  

   the 
  "folioles 
  interradiaux 
  " 
  of 
  de 
  Loriol, 
  are 
  triangular 
  in 
  section, 
  but 
  

   the 
  apex 
  of 
  the 
  triangle 
  is 
  directed 
  inwards, 
  and 
  not 
  outwards 
  as 
  in 
  

   our 
  specimens 
  of 
  Trigonocrinus. 
  In 
  most 
  Eugeniacrini 
  the 
  con- 
  

   joined 
  processes 
  are 
  shaped 
  like 
  spear-heads 
  (fer-de-lance), 
  they 
  are 
  

   more 
  developed 
  and 
  attain 
  a 
  greater 
  length 
  in 
  Phyllocrinus 
  ; 
  this 
  is, 
  

   indeed, 
  the 
  main 
  difference 
  between 
  the 
  two 
  genera. 
  Their 
  rela- 
  

   tively 
  elongate 
  character 
  in 
  Trigonocrinus 
  is 
  the 
  main 
  point 
  of 
  re- 
  

   semblance 
  between 
  this 
  genus 
  and 
  Phyllocrinus 
  (PL 
  VI. 
  fig. 
  12). 
  

  

  The 
  notch 
  (echancrure 
  radiale) 
  between 
  each 
  pair 
  of 
  petals 
  which 
  

   bears 
  the 
  articular 
  facet 
  for 
  the 
  second 
  radial 
  is 
  in 
  Phyllocrinus 
  

   extremely 
  narrow, 
  while 
  the 
  facet 
  occupies 
  the 
  whole 
  thickness 
  of 
  

   the 
  first 
  radial, 
  and 
  is 
  not 
  so 
  deeply 
  sculptured 
  as 
  in 
  Eug. 
  caryo- 
  

   phyllatus 
  (see 
  PL 
  VI. 
  fig. 
  13). 
  The 
  arms 
  in 
  Phyllocrinus 
  must 
  have 
  

   been 
  very 
  thin, 
  and 
  de 
  Loriol 
  hazards 
  the 
  conjecture 
  that 
  they 
  did 
  not 
  

  

  * 
  M. 
  R. 
  Eosinus, 
  ' 
  Tentaminis 
  de 
  Lithozois 
  . 
  . 
  . 
  Prodronius, 
  sive 
  de 
  Stellis 
  

   Marinis,' 
  &c. 
  tab. 
  iii. 
  Classis 
  B, 
  No. 
  3 
  (Hamburg, 
  1719). 
  

  

  t 
  See 
  Appendix, 
  p. 
  167. 
  

  

  \ 
  " 
  Prodrome 
  dune 
  Monographie 
  des 
  Radiaires 
  ou 
  Echinodermes." 
  Mem. 
  

   Soc. 
  Sci. 
  Nat. 
  Neuchatel, 
  i. 
  (1835), 
  pp. 
  168-199(1836) 
  : 
  on 
  pp. 
  195-6, 
  sub 
  Euge- 
  

   niacrinus, 
  and 
  footnote 
  (1). 
  

  

  