﻿PALEONTOLOGY. 
  

  

  have 
  been 
  considered 
  individually, 
  either 
  the 
  various 
  form* 
  have 
  

   been 
  interpreted 
  as 
  distinct 
  Bpecies, 
  or 
  in 
  some 
  instances 
  they 
  have 
  

   been 
  regarded 
  as 
  the 
  representatives 
  of 
  distinct 
  genera. 
  This 
  has 
  

   given 
  rise 
  to 
  the 
  establishment 
  of 
  generic 
  groups 
  which 
  already 
  we 
  

   the 
  necessity 
  of 
  abandoning, 
  while 
  the 
  specific 
  forms 
  are 
  largely 
  

   curtailed 
  by 
  their 
  association 
  into 
  well-defined 
  categories 
  embracing 
  

   two, 
  three, 
  and 
  even 
  four 
  distinct 
  forms, 
  all 
  pertaining 
  to 
  a 
  single 
  

   3. 
  There 
  can 
  no 
  longer 
  remain 
  a 
  doubt 
  as 
  to 
  the 
  specific 
  

   identity 
  of 
  the 
  four 
  forms 
  which 
  Messrs. 
  Newberry 
  and 
  Worthen 
  

   described 
  under 
  the 
  head 
  of 
  CochUodUu 
  nobiU* 
  (('<»■//. 
  l<itus\ 
  of 
  Dr. 
  

   LeidyJ: 
  and 
  yet 
  we 
  are 
  here 
  furnished 
  three 
  groups 
  formerly 
  regarded 
  

   as 
  possessing 
  generic 
  importance, 
  viz: 
  CochHodut, 
  Streblodus, 
  and 
  

   Helodus, 
  in 
  part. 
  The 
  announcement 
  of 
  Professor 
  Richard 
  Owen 
  of 
  

   the 
  discovery 
  of 
  a 
  third 
  mandibular 
  form 
  of 
  Cochliodua 
  (the 
  pre- 
  

   cise 
  nature 
  of 
  which, 
  however, 
  we 
  arc 
  not 
  familiar 
  with) 
  very 
  likely 
  

   will 
  add 
  a 
  fifth 
  form 
  to 
  those 
  already 
  noted 
  under 
  so- 
  called 
  generic 
  

   beade 
  as 
  really 
  belonging 
  to 
  the 
  genus 
  CochHodw. 
  Very 
  nearly 
  the 
  

   Bame 
  state 
  of 
  things 
  obtains 
  in 
  relation 
  to 
  the 
  genera 
  l><lii>ilus, 
  

   Sandalodu8, 
  Pcecilodus, 
  etc. 
  Indeed 
  the 
  various 
  forms 
  of 
  all 
  tl 
  • 
  

   Cochliodont 
  genera 
  have 
  very 
  generally 
  received 
  specific 
  deaignatioi 
  

   while 
  some 
  of 
  them 
  have 
  been 
  identified 
  with 
  genera 
  widely 
  differing 
  

   from 
  one 
  another, 
  as 
  is 
  the 
  case 
  with 
  the 
  forms 
  herein 
  noticed 
  under 
  

   the 
  generic 
  term 
  Orthopleurodnu. 
  

  

  While 
  the 
  facts 
  elicited 
  by 
  the 
  atratigraphical 
  knowledge 
  aocom* 
  

   panying 
  the 
  greater 
  part 
  of 
  the 
  materials 
  aabmitted 
  to 
  us 
  have 
  

   rendered 
  possible, 
  indeed 
  necessitated 
  the 
  revision 
  of 
  tin- 
  genera 
  of 
  

   the 
  Cochliodonts, 
  it 
  has 
  also 
  developed 
  interesting 
  ami 
  important 
  

   facts 
  bearing 
  on 
  the 
  derivation 
  and 
  relations 
  of 
  these 
  genera. 
  That 
  

  

  these 
  may 
  he 
  made 
  comprehensible 
  in 
  briefest 
  statement, 
  the 
  suh- 
  

   joined 
  tabular 
  review 
  of 
  the 
  geological 
  formations 
  immediately 
  con- 
  

  

  oerned, 
  may 
  not 
  be 
  inadmissible 
  in 
  this 
  place. 
  

  

  Table 
  of 
  Carboniferous 
  formations, 
  as 
  developed 
  in 
  the 
  region 
  of 
  

   the 
  Upper 
  M 
  ppi 
  : 
  

  

  M 
  

  

  I 
  ,.,...,( 
  nrl 
  if.'rnu 
  

  

  Klndi 
  i 
  hook 
  t>< 
  

  

  