﻿190 
  Beecher 
  — 
  Natural 
  Classification 
  of 
  the 
  Trilobites. 
  

  

  Una 
  Bergeron, 
  Bavarilla 
  Barrande, 
  Bergeronia 
  Matthew, 
  

   Boeckia 
  Brogger, 
  Ceratopyge 
  Corda, 
  Ohariocephalus 
  Hall, 
  

   Corynexochus 
  Angelin, 
  Crepicephalus 
  Owen, 
  Ctenopyge 
  Lin- 
  

   narsson, 
  Cyclognathus 
  Linnarsson, 
  Pikelocephalus 
  Owen 
  (Oen- 
  

   tropleura 
  Angelin), 
  Dorypyge 
  Dames, 
  Ellipsocephalus 
  Zenker, 
  

   Elliptocephala 
  Emmons, 
  Euloma 
  Angelin, 
  Eurycare 
  Angelin, 
  

   Holmia 
  Matthew, 
  Hydrocephalics 
  Barrande 
  (= 
  young 
  Para- 
  

   doxides), 
  Leptoplastus 
  Angelin, 
  Liostracus 
  Angelin, 
  Logan- 
  

   ellus 
  Devine, 
  Menocephalus 
  Owen, 
  Mesonacis 
  Walcott, 
  Mic- 
  

   macca 
  Matthew, 
  Neseuretus 
  Hicks, 
  Olenelloides 
  Peach 
  r 
  

   Olenellus 
  Hall, 
  Olenoides 
  Meek, 
  Ory 
  otocephalus 
  Walcott, 
  

   Paloeopyge 
  Salter, 
  Parabolina 
  Salter, 
  Paraholinella 
  Brog- 
  

   ger, 
  Paradoxides 
  Brongniart, 
  Peltura 
  Angelin, 
  Plutonides 
  

   Hicks, 
  Proceratopyge 
  Wallerius, 
  Protagraulus 
  Matthew, 
  

   Protolenus 
  Matthew, 
  Protopeltura 
  Brogger, 
  Protypus 
  Wal- 
  

   cott, 
  Pterocephalia 
  Roemer, 
  Ptychaspis 
  Hall, 
  Ptychoparia 
  

   Corda, 
  Eemopleurides 
  Portlock, 
  Sao 
  Barrande, 
  tichmidtia 
  

   Marcou, 
  Solenopleura 
  Angelin, 
  Sphceropthahnus 
  Angelin, 
  

   Telephics 
  Barrande, 
  Triarthrella 
  Hall, 
  Triarthrus 
  Green, 
  

   and 
  Zacanthoides 
  Walcott. 
  

  

  A 
  complete 
  study 
  of 
  this 
  extensive 
  family 
  of 
  trilobites 
  

   would 
  contribute 
  much 
  in 
  the 
  way 
  of 
  generic 
  synonymy, 
  and 
  

   bring 
  out 
  the 
  characters 
  necessary 
  for 
  family 
  determination 
  

   and 
  subdivision. 
  This 
  important 
  work 
  must 
  be 
  left 
  for 
  future 
  

   investigation. 
  So 
  many 
  genera 
  have 
  been 
  described 
  from 
  sep- 
  

   arate 
  cranidia 
  or 
  even 
  pygidia 
  as 
  to 
  make 
  it 
  impossible 
  to 
  deal 
  

   with 
  all 
  of 
  them 
  in 
  a 
  systematic 
  manner. 
  The 
  zeal 
  to 
  make 
  

   the 
  most 
  out 
  of 
  the 
  earliest 
  known 
  faunas 
  has 
  led 
  many 
  inves- 
  

   tigators 
  to 
  describe 
  and 
  recognize 
  imperfect 
  and 
  poorly 
  pre- 
  

   served 
  material, 
  and 
  to 
  establish 
  genera 
  upon 
  very 
  tenuous 
  

   characters. 
  Therefore, 
  without 
  a 
  most 
  intimate 
  knowledge 
  of 
  

   all 
  the 
  forms, 
  any 
  grouping 
  of 
  the 
  majority 
  of 
  the 
  Cambrian 
  

   genera 
  into 
  families 
  or 
  the 
  limitations 
  of 
  the 
  genera 
  them- 
  

   selves 
  must, 
  as 
  in 
  the 
  present 
  instance, 
  be 
  taken 
  tentatively 
  and 
  

   as 
  necessarily 
  incomplete. 
  

  

  A 
  number 
  of 
  genera 
  have 
  already 
  been 
  made 
  the 
  types 
  of 
  

   family 
  divisions, 
  as 
  Paradoxides, 
  Olenellus, 
  Remopleurides, 
  

   Ellipsocephalus, 
  Ptychoparia, 
  etc. 
  Some 
  of 
  them 
  may 
  be 
  

   shown 
  ultimately 
  to 
  possess 
  characters 
  of 
  sufficient 
  weight 
  to 
  

   be 
  entitled 
  to 
  family 
  distinction. 
  A 
  preliminary 
  grouping 
  of 
  

   the 
  best 
  known 
  genera 
  may 
  be 
  of 
  some 
  value 
  here, 
  and 
  for 
  

   the 
  sake 
  of 
  convenience, 
  these 
  divisions 
  may 
  be 
  defined 
  as 
  sub- 
  

   families. 
  Four 
  groups 
  will 
  be 
  recognized, 
  of 
  which 
  Paradox- 
  

   ides, 
  Or 
  y 
  otocephalus, 
  Olenus, 
  and 
  Dikeloceplialus 
  are 
  taken 
  as 
  

   representative 
  genera. 
  

  

  

  