﻿Vol. 
  53.] 
  PETALOGRAPTUS 
  AND 
  CEPHALOGRAPTT7S. 
  197 
  

  

  are 
  short 
  tubes 
  ^ 
  T 
  inch 
  long, 
  and 
  are 
  twice 
  as 
  long 
  as 
  broad. 
  Their 
  

   outer 
  walls 
  are 
  free 
  for 
  a 
  small 
  fraction 
  of 
  their 
  length. 
  The 
  thecse 
  

   are 
  often 
  seen 
  to 
  be 
  adorned 
  with 
  striae 
  parallel 
  to 
  the 
  direction 
  of 
  the 
  

   apertures, 
  which 
  are 
  concave 
  and 
  perpendicular 
  to 
  the 
  long 
  axis 
  of 
  

   each 
  theca, 
  but 
  oblique 
  to 
  the 
  general 
  direction 
  of 
  the 
  rhabdosoma 
  

   (PI. 
  XIV. 
  fig. 
  10). 
  The 
  thecae 
  are 
  widest 
  at 
  their 
  apertures 
  ; 
  they 
  

   are 
  inclined 
  at 
  a 
  constant 
  angle 
  of 
  about 
  35°. 
  The 
  earliest 
  thecse 
  

   are 
  curved 
  very 
  slightly, 
  but 
  subsequent 
  ones 
  are 
  almost 
  straight. 
  

   There 
  are 
  about 
  36 
  apertures 
  in 
  the 
  space 
  of 
  an 
  inch. 
  A 
  septum 
  

   is 
  present, 
  but 
  it 
  seems 
  to 
  be 
  only 
  a 
  partial 
  one. 
  The 
  virgula 
  is 
  

   often 
  distally 
  prolonged. 
  

  

  General 
  Characters. 
  — 
  This 
  variety 
  differs 
  from 
  P.palmeus 
  (restr.), 
  

  

  (1) 
  In 
  its 
  extreme 
  narrowness 
  ; 
  

  

  (2) 
  In 
  the 
  number 
  of 
  thecal 
  apertures 
  in 
  the 
  space 
  of 
  an 
  inch 
  ; 
  

  

  (3) 
  The 
  shortness 
  of 
  the 
  thecse 
  and 
  the 
  absence 
  of 
  curvature 
  ; 
  

  

  (4) 
  The 
  proportions 
  of 
  the 
  thecse. 
  

  

  Horizon. 
  — 
  This 
  variety 
  ranges 
  from 
  the 
  top 
  of 
  the 
  zone 
  of 
  M. 
  

   gregarius 
  (Lapw.) 
  into 
  the 
  Lower 
  Gala-Tarannon 
  Shales. 
  

  

  It 
  occurs 
  with 
  M. 
  convolutus 
  in 
  Scandinavia, 
  at 
  Tommarp, 
  Host- 
  

   anga, 
  Kongslena, 
  and 
  Enan. 
  In 
  Bohemia 
  it 
  occurs 
  with 
  an 
  Upper 
  

   Birkhill 
  fauna 
  at 
  Berown, 
  Zelkovice, 
  etc., 
  and 
  with 
  M. 
  turriculatus 
  

   at 
  Litohlav. 
  

  

  It 
  also 
  occurs 
  in 
  the 
  Pastrites-Shales 
  of 
  Heinrichsruhe 
  in 
  

   Thuringia. 
  

  

  British 
  Localities. 
  — 
  Moffat 
  District 
  : 
  Dobb's 
  Linn, 
  Belcraig, 
  etc. 
  

   Lake 
  District: 
  Skelgill, 
  Pull 
  Beck. 
  Wales: 
  Lower 
  Tarannon- 
  

   Shales, 
  Conway. 
  

  

  P. 
  palmetjs, 
  var. 
  ovato-elongatus 
  (Kurck). 
  (PI. 
  XIV. 
  figs. 
  11-14.) 
  

  

  1850. 
  Diplograptus 
  pahneus, 
  Barraude, 
  ' 
  Grap. 
  de 
  Boheme,' 
  i. 
  pi. 
  iii. 
  fig. 
  7. 
  

  

  1852. 
  Petalolithus 
  pahneus, 
  Suss, 
  'Ueber 
  Bohmische 
  Grapt.' 
  pi. 
  viii. 
  fig. 
  1. 
  

  

  1868. 
  D. 
  pahneus, 
  Nicholson, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxiv. 
  p. 
  523 
  & 
  pi. 
  xix. 
  

   figs. 
  2, 
  3. 
  

  

  1876. 
  D. 
  palmeus, 
  Lapworth, 
  'Cat. 
  Western 
  Scottish 
  Fossils,' 
  pi. 
  i. 
  fig. 
  27. 
  

  

  1881. 
  Cephalograptits 
  ovato-elongatus, 
  Kurck, 
  'Nagra 
  nya 
  Graptolitarter 
  fran 
  

   Sklne,' 
  Geol. 
  Foren. 
  Forhandl. 
  vol. 
  vi. 
  p. 
  303, 
  pi. 
  xiv. 
  fig. 
  10. 
  

  

  1890. 
  D. 
  ovato-elongatus, 
  Geinitz, 
  'Graptoliten 
  des 
  k. 
  Mineralog. 
  Mus. 
  Dresden,' 
  

   pi. 
  A. 
  fig. 
  40. 
  

  

  When 
  Kurck 
  described 
  this 
  form 
  in 
  1881, 
  he 
  acknowledged 
  that 
  

   he 
  was 
  ignorant 
  of 
  any 
  of 
  the 
  details 
  of 
  the 
  structure 
  of 
  the 
  proximal 
  

   end. 
  Had 
  he 
  been 
  acquainted 
  with 
  these 
  he 
  would 
  surely 
  have 
  

   detected 
  the 
  very 
  close 
  relationship 
  existing 
  between 
  this 
  form 
  and 
  

   Petalograptus 
  palmeus, 
  var. 
  latus 
  (Barr.), 
  and 
  would 
  probably 
  then 
  

   have 
  described 
  the 
  form 
  merely 
  as 
  another 
  variety 
  of 
  P. 
  pahneus 
  

   (Barr.). 
  

  

  Structure 
  of 
  the 
  Proooimal 
  End. 
  — 
  The 
  sicula 
  is 
  distinctly 
  seen 
  in 
  

   many 
  specimens 
  ; 
  it 
  is 
  rather 
  less 
  than 
  T 
  ^ 
  inch 
  long 
  and 
  is 
  placed 
  

   exactly 
  as 
  in 
  P. 
  palmeus, 
  var. 
  latus 
  (Barr.), 
  except 
  that 
  in 
  this 
  

  

  