﻿Beecher 
  — 
  Structure 
  and 
  Appendages 
  of 
  Trinucleus. 
  307 
  

  

  Art. 
  XXYII. 
  — 
  Structure 
  and 
  Appendages 
  of 
  Trinucleus 
  / 
  

   by 
  Charles 
  E. 
  Beecher. 
  (With 
  Plate 
  III.) 
  

  

  Trinucleus 
  departs 
  so 
  widely 
  from 
  the 
  common 
  type 
  of 
  

   trilobite 
  form, 
  that 
  any 
  contribution 
  of 
  new 
  facts 
  regarding 
  its 
  

   structure 
  and 
  appendages 
  is 
  a 
  matter 
  of 
  interest. 
  Moreover, 
  

   this 
  added 
  information 
  will 
  be 
  of 
  assistance 
  in 
  interpreting 
  

   some 
  peculiar 
  and 
  striking 
  features 
  in 
  the 
  natural 
  group 
  of 
  

   genera 
  of 
  which 
  Trinucleus 
  is 
  evidently 
  a 
  member. 
  

  

  For 
  the 
  present, 
  it 
  is 
  convenient 
  to 
  consider 
  in 
  this 
  group 
  

   such 
  forms 
  as 
  Trinucleus, 
  Harpes, 
  Harpides, 
  Dionide, 
  and 
  

   Ampyx. 
  Most 
  of 
  these 
  have 
  the 
  genal 
  angles 
  extending 
  to 
  or 
  

   beyond 
  the 
  pygidium, 
  with 
  a 
  broad, 
  finely 
  perforated 
  or 
  punc- 
  

   tate 
  margin 
  around 
  the 
  head. 
  They 
  are 
  further 
  characterized 
  

   by 
  the 
  absence 
  or 
  obsolescence 
  of 
  visual 
  organs, 
  while 
  the 
  facial 
  

   sutures 
  are 
  either 
  peripheral, 
  as 
  in 
  Harpes, 
  or 
  in 
  addition 
  

   include 
  the 
  genal 
  spines, 
  as 
  in 
  Trinucleus, 
  Dionide, 
  and 
  

   Ampyx. 
  Several 
  other 
  genera 
  have 
  been 
  recognized 
  as 
  having 
  

   affinities 
  with 
  those 
  mentioned, 
  but 
  they 
  are 
  imperfectly 
  

   known, 
  and 
  will 
  be 
  merely 
  noticed 
  here. 
  Harpina, 
  Novak, 
  

   based 
  upon 
  the 
  features 
  of 
  the 
  hypostoma, 
  is 
  probably 
  of 
  only 
  

   subgeneric 
  value 
  under 
  Harpes. 
  Arraphus, 
  Angelin, 
  is 
  appar- 
  

   ently 
  based 
  upon 
  a 
  specimen 
  of 
  Harpes 
  denuded 
  of 
  the 
  punc- 
  

   tate 
  border. 
  Salteria 
  of 
  W. 
  Thompson, 
  and 
  Endymionia 
  of 
  

   Billings, 
  both 
  generally 
  considered 
  as 
  closely 
  related 
  to 
  Dio- 
  

   nide, 
  were 
  founded 
  upon 
  too 
  imperfect 
  material 
  to 
  afford 
  

   decisive 
  data 
  as 
  to 
  their 
  affinities. 
  Angelin's 
  sub-genera 
  of 
  

   Ampyx 
  (Zonchodomus, 
  Raphiophorus, 
  and 
  Ampyx) 
  are 
  based 
  

   upon 
  the 
  length 
  of 
  the 
  glabellar 
  spine, 
  and 
  the 
  possession 
  of 
  

   five 
  or 
  six 
  free 
  thoracic 
  segments. 
  Similar 
  characters 
  in 
  

   Trinucleus 
  are 
  not 
  considered 
  as 
  worthy 
  of 
  such 
  marked 
  dis- 
  

   tinction. 
  

  

  In 
  1847, 
  Salter* 
  illustrated 
  and 
  described 
  an 
  eye-tubercle 
  on 
  

   each 
  cheek 
  of 
  Trinucleus, 
  from 
  which 
  there 
  was 
  a 
  raised 
  line 
  

   extending 
  obliquely 
  upward 
  to 
  a 
  punctum 
  or 
  spot 
  on 
  each 
  

   side 
  of 
  the 
  glabella. 
  He 
  considered 
  this 
  line 
  as 
  a 
  discontinuous 
  

   facial 
  suture, 
  but 
  the 
  true 
  suture 
  was 
  afterwards 
  correctly 
  

   determined 
  by 
  Barrande,f 
  and 
  in 
  well-preserved 
  specimens, 
  

   may 
  easily 
  be 
  observed, 
  extending 
  around 
  the 
  entire 
  frontal 
  

   and 
  lateral 
  border 
  of 
  the 
  head, 
  and 
  including 
  the 
  genal 
  

   spines. 
  The 
  "eye-line" 
  was 
  further 
  recognized 
  by 
  McCoy, 
  % 
  

  

  * 
  On 
  the 
  structure 
  of 
  Trinucleus, 
  with 
  Remarks 
  on 
  the 
  Species, 
  Quar. 
  Jour. 
  

   Geol. 
  Soc, 
  vol. 
  iii. 
  pp. 
  251-254. 
  

   fSyst. 
  Sil. 
  Boheme, 
  I.. 
  1852. 
  

   X 
  Ann. 
  Mag. 
  Nat. 
  Hist., 
  2d 
  Series, 
  vol. 
  iv., 
  1849. 
  

  

  