﻿Report 
  of 
  the 
  State 
  Geologist. 
  979 
  

  

  Kayseria, 
  Davidson. 
  1892. 
  

   (Plate 
  36, 
  figs. 
  1, 
  2.) 
  

  

  Shell 
  small, 
  with 
  depressed-convex 
  or 
  lenticular 
  valves, 
  radially 
  

   plicated 
  exterior 
  and 
  a 
  median, 
  plicated 
  sinus 
  on 
  both 
  valves. 
  

   On 
  the 
  interior 
  the 
  pedicle-valve 
  bears 
  a 
  low, 
  thickened 
  median 
  

   ridge, 
  but 
  is 
  otherwise 
  devoid 
  of 
  pronounced 
  peculiarities. 
  In 
  

   the 
  brachial 
  valve 
  there 
  is 
  a 
  high 
  median 
  septum 
  which 
  arises 
  

   from 
  beneath 
  the 
  divided 
  hinge-plate 
  and 
  reaches 
  its 
  greatest 
  

   elevation 
  at 
  a 
  point 
  behind 
  the 
  center 
  of 
  the 
  valve, 
  whence 
  it 
  

   descends 
  rather 
  abruptly, 
  traversing 
  altogether 
  about 
  two-thirds 
  

   the 
  length 
  of 
  the 
  valve. 
  

  

  The 
  spiral 
  cones 
  form 
  sharp 
  angles 
  with 
  the 
  crura, 
  and 
  are 
  

   directed 
  laterally; 
  the 
  jugum 
  is 
  very 
  stout, 
  taking 
  its 
  origin 
  at 
  

   about 
  one-third 
  the 
  length 
  of 
  the 
  primary 
  ribbon 
  ; 
  it 
  is 
  directed 
  

   somewhat 
  posteriorly, 
  its 
  lateral 
  elements 
  uniting 
  to 
  form 
  a 
  short 
  

   saddle 
  which 
  rests 
  upon, 
  and 
  is 
  supported 
  by 
  the 
  most 
  elevated 
  

   part 
  of 
  the 
  median 
  septum. 
  Posteriorly 
  the 
  jugum 
  is 
  continued 
  

   into 
  an 
  upright 
  simple 
  stem, 
  which 
  is 
  

   continued 
  completely 
  across 
  the 
  um- 
  

   bonal 
  cavity 
  and 
  comes 
  into 
  contact 
  

   with 
  the 
  opposite 
  valve, 
  resting 
  upon 
  

   the 
  median 
  ridge 
  of 
  that 
  valve 
  or 
  

   with 
  its 
  extremity 
  inserted 
  into 
  a 
  J 
  IG 
  - 
  fj-- 
  Approximate 
  determin- 
  

  

  « 
  y 
  atioii 
  of 
  the 
  jugum 
  m 
  Kayseria 
  lens, 
  

  

  groove 
  upon 
  that 
  ridge. 
  The 
  acces- 
  Phuiips 
  (s 
  P 
  .). 
  

   sory 
  lamellae 
  originate 
  from 
  a 
  posterior 
  elevation 
  or 
  process 
  arising 
  

   from 
  the 
  saddle 
  of 
  the 
  jugum 
  and 
  are 
  given 
  off 
  at 
  points 
  just 
  in 
  

   front 
  of 
  the 
  crural 
  angles. 
  The 
  ribbon 
  of 
  the 
  principal 
  spiral 
  

   cones 
  is 
  comparatively 
  broad, 
  thickened 
  on 
  the 
  inner 
  margins, 
  

   making 
  six 
  or 
  seven 
  volutions 
  in 
  a 
  full-grown 
  shell. 
  The 
  acces- 
  

   sory 
  lamellae 
  are 
  also 
  produced 
  into 
  spirals 
  which 
  though 
  more 
  

   delicate 
  are 
  composed 
  of 
  as 
  many 
  volutions 
  as 
  the 
  principal 
  spirals. 
  

   At 
  their 
  outset 
  the 
  branches 
  of 
  the 
  accessory 
  lamellae 
  pass 
  

   between 
  the 
  first 
  and 
  second 
  volutions 
  of 
  the 
  principal 
  ribbon, 
  

   and 
  the 
  two 
  are 
  inter 
  coiled 
  in 
  this 
  manner 
  for 
  their 
  entire 
  

   extent. 
  

  

  Type, 
  Kayseria 
  lens, 
  Phillips 
  (sp.). 
  Middle 
  Devonian. 
  

  

  But 
  a 
  single 
  species 
  is 
  known. 
  

  

  37 
  

  

  