﻿E. 
  Bbse 
  — 
  Ammonoids. 
  53 
  

  

  viduals. 
  An 
  immature 
  specimen 
  of 
  about 
  7mm. 
  diameter 
  

   shows 
  one 
  constriction 
  in 
  G. 
  ivelleri 
  and 
  three 
  in 
  our 
  

   species. 
  The 
  cross-section 
  of 
  such 
  a 
  specimen 
  is 
  sub- 
  

   quadrangular 
  in 
  G. 
  welleri 
  and 
  nearly 
  semicircular 
  in 
  

   ours. 
  

  

  There 
  is 
  little 
  if 
  any 
  difference 
  in 
  the 
  sutures 
  of 
  adults 
  

   in 
  both 
  species, 
  but 
  the 
  young 
  ones 
  are 
  much 
  more 
  dis- 
  

   tinct, 
  those 
  of 
  G. 
  welleri 
  showing 
  more 
  archaic 
  features 
  

   than 
  those 
  of 
  the 
  species 
  from 
  New 
  Mexico. 
  

  

  While 
  Hyatt 
  regarded 
  Gonioloboceras 
  as 
  belonging 
  to 
  

   the 
  family 
  Magnosellaridse, 
  J. 
  P. 
  Smith 
  has 
  shown 
  that 
  

   the 
  suture 
  of 
  immature 
  specimens 
  of 
  G. 
  ivelleri 
  has 
  the 
  

   character 
  of 
  Muensteroceras, 
  a 
  genus 
  from 
  the 
  Lower 
  

   Carboniferous, 
  probably 
  derived 
  from 
  Aganides 
  (Bran- 
  

   ooceras 
  Hyatt 
  1884, 
  not 
  Steinmann 
  1881), 
  and 
  belonging 
  

   to 
  the 
  family 
  Glyphioceratidse. 
  I 
  have 
  been 
  able 
  to 
  con- 
  

   firm 
  these 
  observations 
  of 
  Smith 
  by 
  others 
  made 
  on 
  the 
  

   young 
  of 
  our 
  species 
  from 
  Tularosa. 
  An 
  immature 
  

   individual 
  of 
  about 
  10mm. 
  diameter 
  already 
  shows 
  some 
  

   marked 
  differences 
  from 
  the 
  adults. 
  The 
  flanks 
  are 
  

   slightly 
  rounded 
  and 
  the 
  venter 
  is 
  rather 
  broad 
  and 
  

   rounded, 
  the 
  cross-section 
  being 
  helmet-shaped. 
  The 
  

   whorls 
  are 
  deeply 
  embracing 
  but 
  indented 
  to 
  only 
  one- 
  

   fourth 
  by 
  the 
  preceding 
  volution. 
  The 
  border 
  of 
  the 
  

   umbilicus 
  shows 
  a 
  rather 
  sharp 
  edge 
  and 
  the 
  wall 
  has 
  an 
  

   inclination 
  of 
  45 
  degrees, 
  while 
  that 
  of 
  the 
  adult 
  has 
  a 
  

   rounded 
  border 
  and 
  its 
  wall 
  is 
  less 
  steep. 
  The 
  immature 
  

   individual 
  has 
  an 
  ornamentation 
  consisting 
  of 
  fine 
  sig- 
  

   moidal 
  lines 
  on 
  the 
  flank 
  which 
  on 
  the 
  venter 
  suddenly 
  

   curve 
  strongly 
  backwards. 
  The 
  specimen 
  shows 
  one 
  con- 
  

   striction 
  on 
  the 
  oldest 
  part 
  of 
  the 
  external 
  volution 
  while 
  

   the 
  mature 
  specimens 
  have 
  none 
  at 
  all. 
  The 
  youngest 
  

   part 
  of 
  the 
  immature 
  specimen 
  shows 
  a 
  suture 
  quite 
  

   similar 
  to 
  that 
  of 
  the 
  adults, 
  although 
  the 
  siphonal 
  saddle 
  

   is 
  relatively 
  somewhat 
  lower. 
  But 
  only 
  a 
  quarter 
  of 
  a 
  

   volution 
  backwards, 
  this 
  siphonal 
  saddle 
  is 
  already 
  re- 
  

   duced 
  in 
  size 
  to 
  about 
  one-fourth 
  of 
  the 
  height 
  of 
  the 
  

   external 
  saddle, 
  becomes 
  much 
  narrower 
  and 
  more 
  slen- 
  

   der 
  in 
  shape, 
  and 
  shows 
  a 
  distinct 
  indentation 
  at 
  the 
  

   front 
  end. 
  At 
  the 
  oldest 
  part 
  of 
  the 
  volution 
  this 
  saddle 
  

   is 
  still 
  more 
  reduced 
  and 
  the 
  external 
  saddles 
  become 
  less 
  

   sharp 
  and 
  somewhat 
  rounded 
  at 
  the 
  point. 
  The 
  first 
  

   lateral 
  saddle 
  also 
  becomes 
  gradually 
  lower 
  and 
  rela- 
  

   tively 
  broader. 
  

  

  