﻿994 
  Fobit-seventm 
  Rep 
  obi 
  on 
  tee 
  State 
  Museum. 
  

  

  and 
  then 
  widen 
  again, 
  attaining 
  their 
  greatest 
  width 
  where 
  

   they 
  unite. 
  From 
  their 
  line 
  of 
  union 
  there 
  is 
  a 
  short, 
  acute 
  

  

  and 
  simple 
  process 
  extended 
  horizontally 
  

   backward. 
  The 
  attitude 
  of 
  the 
  jugum 
  

   is 
  erect, 
  at 
  its 
  base 
  extending 
  slightly 
  

   backward 
  and 
  then 
  curving 
  broadly 
  

   forward 
  and 
  upward 
  ; 
  in 
  height, 
  it 
  

   reaches 
  rather 
  more 
  than 
  half-way 
  across 
  

   fig. 
  370.- 
  jugum 
  of 
  Trematos- 
  the 
  bases 
  of 
  the 
  spiral 
  cones. 
  The 
  cones 
  

  

  piramultistriata, 
  H 
  & 
  11 
  ^ 
  situated 
  ag 
  in 
  ^^ 
  genera 
  and 
  the 
  

  

  ribbon, 
  in 
  mature 
  shells, 
  makes 
  nine 
  or 
  ten 
  volutions. 
  Muscular 
  

   impressions 
  indistinct. 
  Shell 
  substance 
  punctate. 
  

  

  Type, 
  Trematospira 
  multistriata, 
  Hall. 
  Lower 
  Helderberg 
  

   group. 
  

  

  Distribution. 
  Upper 
  Silurian 
  — 
  Devonian. 
  

  

  Parazyga, 
  Hall. 
  1893. 
  

  

  (Plate 
  38, 
  figs. 
  13-20.) 
  

  

  Shells 
  similar 
  in 
  general 
  external 
  aspect 
  to 
  Trematospika. 
  

   The 
  surface 
  markings 
  consist 
  of 
  numerous 
  fine, 
  rounded, 
  simple 
  

   ribs, 
  extending 
  alike 
  over 
  median 
  fold 
  and 
  sinus, 
  and 
  these 
  are 
  

   covered 
  with 
  exceedingly 
  fine, 
  short, 
  hair-like 
  spines, 
  which 
  are 
  

   usually 
  broken 
  off, 
  leaving 
  only 
  their 
  bases. 
  

  

  The 
  umbo 
  of 
  the 
  pedicle- 
  valve 
  is 
  closely 
  incurved 
  and 
  the 
  del- 
  

   tarium 
  (or 
  coalesced 
  deltidial 
  plates) 
  which 
  is 
  entirely 
  concealed 
  

   by 
  the 
  umbo 
  of 
  the 
  opposite 
  valve, 
  is 
  usually 
  lost. 
  The 
  apical 
  

   portion 
  of 
  the 
  umbonal 
  cavity 
  bears 
  an 
  introverted 
  lamella 
  which 
  

   forms 
  an 
  incomplete 
  tube 
  like 
  that 
  in 
  Retzia, 
  Hcstedia, 
  etc., 
  but 
  

   of 
  no 
  great 
  extent. 
  The 
  teeth 
  are 
  as 
  in 
  Trkmatospira 
  and 
  are 
  

   supported 
  by 
  stout 
  plates. 
  The 
  muscular 
  area 
  is 
  short, 
  rather 
  

   well 
  defined, 
  and 
  is 
  divided 
  into 
  a 
  broad 
  central 
  adductor 
  impres- 
  

   sion, 
  along 
  the 
  lateral 
  margins 
  of 
  which 
  lie 
  two 
  flabellate 
  

   diductor 
  scars. 
  

  

  The 
  hinge-plate 
  is 
  very 
  narrow, 
  and 
  is 
  composed 
  of 
  two 
  ver- 
  

   tical 
  supports 
  which 
  have 
  their 
  origin 
  on 
  the 
  downward 
  umbonal 
  

   slope 
  of 
  the 
  shell. 
  These 
  supports 
  are 
  widely 
  separated 
  at 
  their 
  

   bases 
  and 
  enclose 
  the 
  marginal 
  dental 
  sockets; 
  their 
  anterior 
  

  

  52 
  

  

  