﻿188 
  MISS 
  G. 
  L. 
  ELLES 
  ON 
  THE 
  SUBGENERA 
  [May 
  1 
  897,- 
  

  

  II. 
  Definition 
  op 
  the 
  Subgenera. 
  

   Petalograptus. 
  

  

  Bhabdosoma 
  f 
  oliiform. 
  Sicula 
  embedded, 
  completely 
  visible 
  only 
  

   on 
  one 
  side 
  of 
  the 
  rhabdosoma. 
  Proximal 
  end 
  somewhat 
  protracted, 
  

   never 
  rounded. 
  Thecae 
  of 
  various 
  lengths, 
  all 
  with 
  the 
  same 
  general 
  

   characters. 
  Long 
  tubes 
  with 
  concave 
  apertures, 
  situated 
  obliquely 
  

   to 
  the 
  general 
  direction 
  of 
  the 
  rhabdosoma. 
  Septum 
  complete 
  or 
  

   partial. 
  Type, 
  Petalograptus 
  folium 
  (His.). 
  

  

  To 
  this 
  subgenus 
  may 
  also 
  be 
  referred 
  : 
  — 
  

  

  Petalograptus 
  palmeus 
  (Barr.) 
  ; 
  P. 
  p. 
  var. 
  latus 
  (Barr.) 
  ; 
  P.p. 
  var. 
  

   tenuis 
  (Barr.) 
  ; 
  P.p. 
  var. 
  ovato-elongatus 
  (Kurck) 
  ; 
  P. 
  ovatus 
  (Barr.) 
  ; 
  

   P. 
  minor 
  (sp. 
  nov.). 
  

  

  Cephalograptus. 
  

  

  Bhabdosoma 
  fusiform 
  or 
  triangular. 
  Sicula 
  exposed, 
  completely 
  

   visible 
  on 
  both 
  sides 
  of 
  the 
  rhabdosoma. 
  Proximal 
  end 
  very 
  

   protracted. 
  Thecse 
  long, 
  tubular, 
  with 
  concave 
  apertures 
  almost 
  

   perpendicular 
  to 
  the 
  long 
  axis 
  of 
  the 
  rhabdosoma. 
  Septum 
  incom- 
  

   plete. 
  Type, 
  Cephalograptus 
  cometa 
  (Geinitz) 
  ; 
  also 
  0. 
  petalum, 
  

   sp. 
  nov. 
  

  

  The 
  species 
  are 
  particularly 
  characteristic 
  of 
  the 
  Middle 
  and 
  

   Upper 
  Birkhill 
  Shales 
  ; 
  some 
  survive 
  into 
  the 
  Lower 
  Gala-Tarannon, 
  

   and 
  one 
  appears 
  to 
  be 
  confined 
  to 
  that 
  horizon. 
  

  

  I 
  now 
  proceed 
  to 
  a 
  description 
  of 
  the 
  species, 
  beginning 
  with 
  the 
  

   type-species 
  of 
  the 
  subgenus 
  Petalograptus. 
  

  

  III. 
  Description 
  of 
  the 
  Species. 
  

   Subgenus 
  Petalograptus. 
  

   Petalograptus 
  folium 
  (Hisinger). 
  (PI. 
  XIII. 
  figs. 
  1-5.) 
  

  

  1837. 
  Trionotus 
  folium, 
  Hisinger, 
  'Lethsea 
  Suecica,' 
  Suppl. 
  p. 
  114, 
  pl. 
  xxxv. 
  fig. 
  8. 
  

  

  1843. 
  Prionotus 
  folium, 
  Portlock, 
  ' 
  Geol. 
  Keport 
  Londonderry,' 
  p. 
  321, 
  pi. 
  xx. 
  fig. 
  6. 
  

  

  1851. 
  Non 
  Divrion 
  folium, 
  Harkness, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  vii. 
  p. 
  63 
  pi 
  i. 
  

   fig. 
  12. 
  

  

  1851. 
  Non 
  Diplogr. 
  folium, 
  Scharenberg, 
  ' 
  Ueber 
  Graptolithen,' 
  p. 
  16, 
  pi. 
  i. 
  figs. 
  13 
  

   14, 
  pi. 
  ii. 
  figs. 
  15, 
  16. 
  

  

  1851. 
  Non 
  Trionotus 
  folium, 
  Bceck, 
  ' 
  Bemgerkninger 
  angaaende 
  Graptolitherne/ 
  

   pi. 
  i. 
  fig. 
  8. 
  

  

  1868. 
  Non 
  Diplogr. 
  folium, 
  Nicholson, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxiv. 
  p. 
  524, 
  

   pl. 
  xix. 
  figs. 
  4-7. 
  

  

  1868. 
  Non 
  Diplogr. 
  folium, 
  Carrutbers, 
  ' 
  Syst. 
  Position 
  of 
  the 
  Graptolites,' 
  

   Intellectual 
  Observer, 
  xi. 
  pl. 
  ii. 
  figs. 
  4>a~e, 
  5 
  a-d. 
  

  

  1876. 
  Non 
  Diplogr. 
  folium, 
  Lapworth, 
  ' 
  Grap. 
  of 
  Co. 
  Down,' 
  Proc. 
  Belfast 
  

   Naturalists' 
  Field 
  Club, 
  p. 
  133, 
  pl. 
  vi. 
  fig. 
  16. 
  

  

  1880. 
  Diplogr. 
  folium, 
  Tornquist, 
  Geol. 
  Foren. 
  Forhandl. 
  vol. 
  v. 
  p. 
  442, 
  pl. 
  xvii 
  

   fig. 
  7. 
  

  

  1882. 
  Cephalogr. 
  folium, 
  Tullberg, 
  K. 
  Svenska 
  Vet. 
  Akad. 
  Handl. 
  vol. 
  vi. 
  no. 
  13. 
  

   p. 
  15, 
  pl. 
  i. 
  figs. 
  15-19. 
  

  

  1890. 
  Diplogr. 
  folium, 
  Geinitz, 
  ' 
  Graptoliten 
  des 
  k. 
  Mineralog. 
  Mus. 
  Dresden,' 
  

   p. 
  26, 
  pl. 
  A. 
  figs. 
  44-46. 
  

  

  