﻿52 
  E. 
  Bose 
  — 
  Ammonoids. 
  

  

  belong 
  to 
  well 
  known 
  and 
  characteristic 
  groups, 
  as 
  will 
  

   be 
  seen 
  in 
  the 
  following 
  pages. 
  

  

  The 
  most 
  important 
  species 
  of 
  our 
  collection 
  belongs 
  

   to 
  Gonioloboceras. 
  This 
  genus 
  was 
  created 
  by 
  Hyatt 
  1 
  

   for 
  a 
  species 
  from 
  New 
  Mexico: 
  Goniatites 
  goniolobus 
  

   Meek, 
  characterized 
  by 
  flattened 
  flanks, 
  narrow 
  rounded 
  

   venter 
  and 
  extremely 
  angular 
  lobes. 
  Unfortunately 
  

   neither 
  the 
  horizon 
  nor 
  the 
  locality 
  where 
  this 
  species 
  

   was 
  found 
  is 
  known, 
  but 
  it 
  is 
  merely 
  said 
  to 
  have 
  come 
  

   from 
  the 
  Carboniferous 
  of 
  New 
  Mexico. 
  

  

  This 
  species 
  is 
  entirely 
  different 
  from 
  ours, 
  notwith- 
  

   standing 
  that 
  Gonioloboceras 
  is 
  a 
  rather 
  rare 
  genus 
  and 
  

   that 
  both 
  forms 
  come 
  from 
  the 
  same 
  state. 
  It 
  has 
  much 
  

   more 
  rounded 
  flanks 
  and 
  the 
  venter 
  is 
  not 
  flattened 
  at 
  all, 
  

   while 
  our 
  species 
  shows 
  extremely 
  flat 
  flanks 
  and 
  in 
  

   mature 
  specimens 
  a 
  flattened 
  venter 
  or 
  even 
  a 
  slight 
  

   longitudinal 
  depression 
  on 
  it, 
  although 
  no 
  real 
  furrow 
  

   seems 
  to 
  be 
  developed 
  in 
  medium 
  sized 
  individuals. 
  The 
  

   whorls 
  of 
  G. 
  goniolobus 
  are 
  deeper 
  embracing, 
  and 
  the 
  

   cross-section 
  is 
  nearly 
  elliptical, 
  while 
  in 
  our 
  species 
  it 
  is 
  

   almost 
  sagittal. 
  The 
  greatest 
  difference, 
  however, 
  exists 
  

   in 
  the 
  suture. 
  On 
  the 
  whole, 
  the 
  lobes 
  of 
  G. 
  goniolobus 
  

   seem 
  to 
  be 
  still 
  more 
  angular, 
  although 
  there 
  is 
  a 
  general 
  

   resemblance. 
  The 
  siphonal 
  saddle 
  which 
  divides 
  the 
  

   ventral 
  lobe 
  in 
  Meek's 
  form 
  is 
  of 
  an 
  entirely 
  different 
  

   shape, 
  — 
  narrower 
  and 
  rather 
  pointed, 
  with 
  an 
  indenta- 
  

   tion 
  at 
  its 
  end, 
  — 
  while 
  in 
  our 
  species 
  it 
  is 
  high 
  and 
  broad, 
  

   with 
  a 
  tongue-like 
  prolongation. 
  

  

  J. 
  P. 
  Smith 
  2 
  has 
  described 
  another 
  species 
  belonging 
  

   to 
  Gonioloboceras, 
  G. 
  welleri, 
  from 
  the 
  Cisco 
  formation 
  

   of 
  central 
  Texas 
  ; 
  and 
  this 
  form 
  is 
  much 
  more 
  intimately 
  

   related 
  to 
  ours. 
  The 
  shape 
  of 
  the 
  shell 
  is 
  very 
  similar, 
  

   but 
  in 
  our 
  species 
  the 
  flanks 
  are 
  still 
  flatter, 
  while 
  the 
  

   venter 
  is 
  generally 
  more 
  rounded 
  and 
  does 
  not 
  show 
  a 
  

   real 
  deep 
  furrow 
  like 
  the 
  adults 
  of 
  G. 
  welleri. 
  Still, 
  the 
  

   flattening 
  of 
  the 
  venter 
  and 
  the 
  development 
  of 
  a 
  slight 
  

   longitudinal 
  depression 
  in 
  our 
  species 
  show 
  that 
  the 
  rela- 
  

   tion 
  between 
  the 
  two 
  is 
  very 
  intimate; 
  they 
  certainly 
  

   belong 
  to 
  the 
  same 
  group 
  although 
  they 
  are 
  specifically 
  

   different. 
  

  

  The 
  greatest 
  difference 
  appears 
  in 
  the 
  younger 
  indi- 
  

  

  X 
  A. 
  Hyatt, 
  in 
  Eastman-Zittel, 
  Textbook 
  of 
  Paleontology, 
  p. 
  551, 
  1900. 
  

   2 
  J. 
  P. 
  Smith, 
  The 
  Carboniferous 
  Ammonoids 
  of 
  America, 
  U. 
  S. 
  Geol. 
  

   Survey, 
  No. 
  42, 
  p. 
  125, 
  pi. 
  20, 
  figs. 
  9-11; 
  pi. 
  21, 
  figs. 
  1-7 
  6, 
  1903. 
  

  

  