﻿56 
  E. 
  Bose 
  — 
  Ammonoids. 
  

  

  The 
  nodules 
  on 
  the 
  umbilical 
  shoulder 
  are 
  scarcely 
  notice- 
  

   able, 
  and 
  the 
  costae 
  on 
  the 
  venter 
  disappear 
  altogether, 
  

   leaving 
  only 
  traces 
  of 
  faint 
  lines 
  of 
  growth 
  ; 
  but 
  in 
  this 
  

   stage 
  of 
  development 
  we 
  observe 
  a 
  very 
  great 
  number 
  of 
  

   fine 
  but 
  distinct 
  spiral 
  costae 
  separated 
  by 
  wide 
  inter- 
  

   stices. 
  On 
  the 
  umbilical 
  shoulder, 
  three 
  or 
  four 
  of 
  these 
  

   spiral 
  lines 
  become 
  very 
  distinct, 
  and 
  their 
  crossing 
  with 
  

   the 
  umbilical 
  ribs 
  and 
  the 
  fine 
  radial 
  costse 
  which 
  dis- 
  

   appear 
  on 
  the 
  venter 
  causes 
  two, 
  three 
  or 
  four 
  rows 
  of 
  

   fine 
  tubercles. 
  These 
  spiral 
  lines 
  can 
  also 
  be 
  observed 
  

   on 
  the 
  well 
  preserved 
  shell 
  of 
  small 
  individuals 
  (5mm. 
  

   diameter 
  and 
  less) 
  but 
  there 
  they 
  are 
  so 
  fine 
  and 
  the 
  

   strong 
  radial 
  sculpture 
  is 
  so 
  prominent 
  that 
  they 
  easily 
  

   escape 
  observation. 
  

  

  In 
  our 
  immature 
  specimens 
  the 
  nodules 
  of 
  the 
  umbil- 
  

   ical 
  shoulder 
  recall 
  somewhat 
  those 
  in 
  G. 
  montgomery- 
  

   ense 
  Miller 
  and 
  Gurley, 
  6 
  but 
  in 
  the 
  larger 
  individuals 
  

   this 
  ornamentation 
  is 
  extremely 
  fine 
  and 
  nearly 
  disap- 
  

   pears 
  on 
  the 
  casts. 
  

  

  Notwithstanding 
  the 
  difference 
  in 
  ornamentation, 
  I 
  

   am 
  inclined 
  to 
  include 
  our 
  species, 
  as 
  well 
  as 
  G. 
  montgom- 
  

   eryense, 
  in 
  the 
  group 
  of 
  G. 
  subcavum, 
  which 
  may 
  have 
  

   descended 
  from 
  forms 
  like 
  G. 
  entogonum 
  of 
  the 
  Missis- 
  

   sippian. 
  

  

  The 
  ornamentation 
  described 
  above 
  nearly 
  disappears 
  

   from 
  casts, 
  and 
  these 
  thus 
  appear 
  remarkably 
  similar 
  

   to 
  G. 
  subcavum. 
  This 
  latter 
  species 
  was 
  first 
  described 
  

   from 
  the 
  upper 
  Pennsylvanian 
  of 
  Montgomery 
  County, 
  

   Illinois, 
  but 
  was 
  also 
  found 
  in 
  the 
  Cisco 
  formation 
  of 
  

   Graham, 
  Young 
  County, 
  Texas, 
  about 
  600 
  feet 
  below 
  the 
  

   contact 
  of 
  the 
  Permian. 
  It 
  is 
  very 
  common 
  in 
  the 
  Abo 
  

   beds 
  of 
  Tularosa, 
  our 
  collection 
  containing 
  at 
  least 
  forty 
  

   specimens 
  of 
  it. 
  It 
  may 
  be 
  known 
  as 
  G. 
  subtilicostatum, 
  

   n. 
  sp. 
  

  

  As 
  we 
  have 
  already 
  mentioned, 
  the 
  genus 
  Gastrioceras 
  

   is 
  represented 
  at 
  our 
  locality 
  by 
  quite 
  a 
  number 
  of 
  spe- 
  

   cies, 
  not 
  all 
  of 
  them 
  as 
  characteristic 
  as 
  the 
  above 
  de- 
  

   scribed 
  type 
  but 
  of 
  sufficient 
  interest 
  to 
  be 
  mentioned 
  

   here. 
  

  

  There 
  are 
  two 
  species 
  which 
  to 
  a 
  certain 
  degree 
  resem- 
  

   ble 
  the 
  one 
  described 
  on 
  the 
  foregoing 
  pages. 
  Both 
  

   have 
  the 
  deep 
  funnel-shaped 
  umbilicus 
  with 
  a 
  rather 
  

   sharp 
  edge 
  on 
  the 
  umbilical 
  border 
  although 
  somewhat 
  

   less 
  than 
  in 
  the 
  preceding 
  form. 
  Both 
  are 
  much 
  less 
  

  

  J. 
  P. 
  Smith, 
  op. 
  cit., 
  p. 
  95, 
  pi. 
  5, 
  figs. 
  8-10. 
  

  

  