﻿638 
  Proceedings. 
  

  

  structure, 
  and 
  tlie 
  internal 
  casts 
  show 
  that 
  a 
  strong 
  septum 
  divided 
  the 
  

   prominent 
  ventral 
  beak 
  into 
  two 
  cavities. 
  

  

  A 
  third 
  form 
  related 
  to 
  Spiriferina 
  in 
  having 
  a 
  punctate 
  shell-structure, 
  

   differs 
  so 
  essentially 
  as 
  to 
  require 
  separation 
  as 
  a 
  genus, 
  to 
  which 
  the 
  

   name 
  Piastelligera 
  has 
  been 
  applied, 
  from 
  the 
  peculiar 
  character 
  of 
  the 
  

   hinge-line, 
  which 
  is 
  enormously 
  long 
  in 
  proportion 
  to 
  the 
  height 
  of 
  

   the 
  shell, 
  and 
  along 
  the 
  hinge-margin 
  both 
  valves 
  are 
  minutely 
  denti- 
  

   culate, 
  with 
  rake-like 
  teeth 
  that 
  appeared 
  to 
  interlock. 
  The 
  proper 
  

   dental 
  processes 
  are 
  only 
  feebly 
  developed, 
  if 
  not 
  altogether 
  absent, 
  

   and 
  both 
  valves 
  are 
  nearly 
  equally 
  convex. 
  The 
  genus 
  East 
  ellig 
  era, 
  of 
  

   which 
  there 
  are 
  several 
  species, 
  is 
  limited 
  to 
  the 
  Wairoa 
  series 
  (Triassic), 
  

   and 
  the 
  Otapiri 
  series 
  (Rhaatic). 
  

  

  The 
  next 
  form, 
  which 
  is 
  like 
  Spiriferina 
  in 
  general 
  outline, 
  although 
  

   in 
  different 
  species 
  it 
  varies 
  greatly 
  in 
  the 
  extension 
  of 
  the 
  hinge-line, 
  

   has 
  a 
  marked 
  pecuharity 
  in 
  the 
  arrangement 
  of 
  the 
  dental 
  plates, 
  

   which 
  spring 
  from 
  the 
  sides 
  of 
  the 
  mesial 
  septum, 
  so 
  that 
  a 
  horizontal 
  

   section 
  of 
  the 
  beak, 
  or 
  the 
  fissures 
  seen 
  in 
  the 
  natural 
  internal 
  cast, 
  show 
  

   the 
  interior 
  processes 
  to 
  have 
  been 
  arranged 
  like 
  the 
  Greek 
  character 
  ;//, 
  

   from 
  which 
  the 
  name 
  Psioidea 
  has 
  been 
  given 
  to 
  the 
  genus. 
  Some 
  of 
  

   the 
  species 
  are 
  remarkable 
  for 
  the 
  great 
  development 
  of 
  a 
  concave 
  triangular 
  

   area, 
  overhung 
  by 
  a 
  strongly 
  projecting 
  dorsal 
  umbo. 
  This 
  genus 
  has 
  been 
  

   discovered 
  in 
  the 
  Silurian 
  formation, 
  and 
  finally 
  disappears 
  in 
  the 
  upper 
  

   part 
  of 
  the 
  Ehsetic 
  beds. 
  

  

  Besides 
  the 
  above, 
  which 
  are 
  all 
  allied 
  to 
  Spiriferina, 
  true 
  forms 
  of 
  

   Athyris 
  (Spirigera) 
  are 
  not 
  uncommon 
  from 
  the 
  Triassic 
  formation 
  down- 
  

   wards 
  ; 
  but 
  in 
  the 
  same 
  formation, 
  and 
  in 
  the 
  overlying 
  Ehfetic 
  (Otapiri) 
  

   series, 
  Athijris 
  is 
  only 
  represented 
  by 
  an 
  allied 
  genus, 
  having 
  also 
  a 
  

   lamenellate 
  shell-structure, 
  but 
  possessing 
  characters 
  that 
  have 
  required 
  

   its 
  separation 
  under 
  the 
  generic 
  name 
  of 
  Clavigera. 
  

  

  This 
  form 
  agrees 
  with 
  Athyris 
  in 
  having 
  the 
  ventral 
  beak 
  foraminate 
  

   and 
  in 
  the 
  apices 
  of 
  the 
  spire-cones 
  being 
  central 
  and 
  directed 
  to 
  the 
  

   middle 
  of 
  the 
  lateral 
  margins, 
  and 
  not 
  to 
  the 
  cardinal 
  angles 
  as 
  in 
  

   Sjnrifera. 
  But 
  it 
  differs 
  in 
  the 
  possession 
  of 
  a 
  distinct 
  area 
  and 
  fissure 
  

   under 
  the 
  beak, 
  and 
  a 
  long, 
  straight 
  hmge-line, 
  in 
  which 
  respect 
  it 
  

   resembles 
  the 
  Spirifera. 
  Its 
  most 
  obvious 
  peculiarity 
  is 
  that 
  both 
  valves 
  

   are 
  almost 
  equally 
  convex, 
  and 
  that 
  both 
  are 
  sulcate 
  in 
  the 
  median 
  line, 
  

   and 
  that 
  both 
  a 
  foramen 
  and 
  a 
  fissure 
  are 
  present 
  in 
  the 
  ventral 
  valve, 
  which 
  

   is 
  a 
  most 
  exceptional 
  character 
  among 
  Spiriferidi^. 
  The 
  name 
  has 
  been 
  

   given 
  on 
  account 
  of 
  the 
  strong 
  stud-shaped 
  cardinal 
  boss, 
  which 
  in 
  the 
  

   cast 
  gives 
  rise 
  to 
  a 
  singular 
  hood-like 
  process, 
  owing 
  to 
  the 
  matrix 
  that 
  

   lodged 
  between 
  the 
  interior 
  surface 
  of 
  the 
  dental-plates 
  and 
  the 
  boss 
  having 
  

   been 
  preserved 
  after 
  the 
  shell 
  has 
  weathered 
  cut. 
  

  

  