﻿Beecher 
  — 
  Natural 
  Classification 
  of 
  the 
  Trilobites. 
  181 
  

  

  Art. 
  XYIII. 
  — 
  Outline 
  of 
  a 
  Natural 
  Classification 
  of 
  the 
  

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

  

  [Continued 
  from 
  page 
  106.] 
  

  

  Arrangement 
  of 
  the 
  

   Subclass 
  

   Order 
  A. 
  

  

  Family 
  1. 
  Agnostidae. 
  

   Family 
  2. 
  Harpedidae. 
  

  

  Families 
  of 
  Trilobites. 
  

   TRILOBITA. 
  

   Hypoparia. 
  

  

  Family 
  3. 
  Trinucleiclae. 
  

  

  Family 
  4. 
  Conocoryphidae 
  

  

  Family 
  5. 
  Olenidae. 
  

  

  Family 
  6. 
  Asaphidae. 
  

  

  Family 
  7. 
  Proeiidae. 
  

  

  Order 
  B. 
  Opisthoparia. 
  

  

  Family 
  8. 
  Bronteidae. 
  

  

  Family 
  9. 
  Lichadidae. 
  

   Family 
  10. 
  Acidaspidae. 
  

  

  Family 
  11. 
  Encrinuridae 
  

   Family 
  12. 
  Calymenidae. 
  

  

  Order 
  C. 
  Proparia. 
  

  

  Family 
  13. 
  Cheiruridae. 
  

  

  Family 
  14. 
  Phacopidae. 
  

  

  The 
  order 
  Opisthoparia, 
  with 
  nearly 
  one 
  hundred 
  and 
  fifty 
  

   genera, 
  has 
  a 
  much 
  greater 
  geological 
  distribution 
  than 
  either 
  

   of 
  the 
  others, 
  and 
  was 
  by 
  far 
  the 
  dominant 
  group 
  during 
  the 
  

   Cambrian 
  and 
  Ordovician, 
  being 
  represented 
  by 
  about 
  eighty- 
  

   five 
  genera 
  in 
  the 
  former 
  age 
  and 
  forty-five 
  in 
  the 
  latter. 
  

   Nineteen 
  genera 
  of 
  this 
  order 
  are 
  found 
  in 
  the 
  Silurian 
  and 
  

   ten 
  in 
  the 
  Devonian, 
  most 
  of 
  them 
  having 
  continued 
  on 
  from 
  

   older 
  ages. 
  Four 
  genera 
  represent 
  the 
  order 
  in 
  the 
  Car- 
  

   boniferous 
  and 
  one 
  in 
  the 
  Permian, 
  thus 
  marking 
  the 
  extinc- 
  

   tion 
  of 
  the 
  subclass 
  as 
  well 
  as 
  the 
  last 
  genera 
  of 
  the 
  

   Opisthoparia. 
  

  

  The 
  comparative 
  abundance 
  and 
  duration 
  of 
  the 
  three 
  orders 
  

   are 
  expressed 
  in 
  the 
  table 
  on 
  page 
  182, 
  from 
  which 
  it 
  appears 
  

   that 
  the 
  Hypoparia 
  probably 
  culminated 
  in 
  pre-Cambrian 
  

   times, 
  the 
  Opisthoparia 
  during 
  the 
  Cambrian, 
  and 
  the 
  Proparia 
  

   during 
  the 
  Ordovician. 
  

  

  In 
  the 
  following 
  classification, 
  the 
  families 
  adopted 
  by 
  Salter 
  88 
  

   and 
  Barrande 
  3 
  are 
  in 
  the 
  main 
  adhered 
  to, 
  and 
  the 
  number 
  cor- 
  

   responds 
  very 
  closely 
  with 
  that 
  in 
  Zittel's 
  " 
  Handbuch 
  der 
  

   Palseontologie 
  " 
  35 
  and 
  also 
  in 
  the 
  " 
  Grundziige 
  " 
  36 
  of 
  the 
  same 
  

   author. 
  The 
  order 
  of 
  arrangement, 
  however, 
  is 
  very 
  different. 
  

   A 
  great 
  number 
  of 
  family 
  divisions 
  have 
  been 
  proposed, 
  and 
  

   undoubtedly 
  many 
  others 
  will 
  yet 
  be 
  made, 
  but 
  it 
  is 
  not 
  within 
  

   the 
  province 
  of 
  this 
  paper 
  to 
  determine 
  the 
  precise 
  value 
  and 
  

  

  Am. 
  Jour. 
  Scl— 
  Fourth 
  Series, 
  Yol. 
  Ill, 
  No. 
  15. 
  

   13 
  

  

  •March, 
  1897. 
  

  

  