﻿^°1' 
  53'] 
  FOSSILS 
  FKOM 
  THE 
  MORTE 
  SLATES, 
  ETC. 
  455 
  

  

  Hinge-line 
  as 
  long 
  as 
  the 
  width, 
  bearing 
  a 
  few 
  large, 
  obliquely-set, 
  

   arching 
  spines. 
  Surface 
  with 
  40 
  or 
  50 
  coarse, 
  rounded, 
  close 
  rays, 
  

   which 
  have 
  increased 
  by 
  intercalation 
  at 
  various 
  distances 
  from 
  the 
  

   umbo. 
  Interior 
  of 
  ventral 
  valve 
  with 
  two 
  strong 
  grooves, 
  reaching 
  

   more 
  than 
  halfway 
  forward, 
  and 
  with 
  several 
  coarse 
  punctations. 
  

   Lateral 
  margins 
  slightly 
  alate 
  where 
  they 
  join 
  the 
  hinge-line. 
  

  

  Remarks, 
  The 
  ribs 
  are 
  coarsely 
  granulate 
  as 
  seen 
  on 
  the 
  inside 
  of 
  

   the 
  dorsal 
  valve, 
  and 
  are 
  crossed 
  by 
  fine 
  regular 
  concentric 
  threads. 
  

   Our 
  shells 
  appear 
  to 
  agree 
  accurately 
  with 
  Oh. 
  plebeia 
  as 
  described 
  

   by 
  Schnur 
  x 
  and 
  (Ehlert 
  2 
  as 
  well 
  as 
  by 
  Kayser, 
  3 
  who 
  first 
  united 
  it 
  

   to 
  Oh. 
  sarcinulata, 
  Schloth., 
  but 
  afterwards, 
  4 
  following 
  (Ehlert, 
  again 
  

   separated 
  it. 
  

  

  At 
  Treborough 
  it 
  seems 
  to 
  have 
  been 
  gregarious, 
  occurring 
  

   abundantly 
  in 
  a 
  different 
  part 
  of 
  the 
  quarry 
  from 
  that 
  which 
  has 
  

   yielded 
  Ch. 
  sarcinulata 
  and 
  most 
  of 
  the 
  other 
  fossils. 
  

  

  Chonetes 
  sarcinulata, 
  Schlotheim, 
  sp. 
  ? 
  (PI. 
  XXXIII. 
  figs. 
  3-5.) 
  

  

  [(Ehlert, 
  Bull. 
  Soc. 
  geol. 
  Erance, 
  ser. 
  3, 
  vol. 
  xi. 
  p. 
  520, 
  remarks 
  : 
  

   ' 
  This 
  species, 
  whose 
  geographical 
  extension 
  is 
  very 
  great, 
  is 
  

   characteristic 
  of 
  the 
  Lower 
  Devonian/] 
  

  

  Locality. 
  Treborough. 
  Eight 
  specimens. 
  

  

  Size. 
  Length 
  11 
  mm., 
  width 
  16 
  mm. 
  

  

  Description. 
  Shell 
  small, 
  transverse, 
  semi-oval. 
  Hinge-line 
  showing 
  

   a 
  double 
  area 
  and 
  a 
  triangular 
  fissure, 
  and 
  bearing 
  a 
  few 
  rather 
  

   large, 
  obliquely-set, 
  arching 
  spines. 
  Muscular 
  area 
  large, 
  heart- 
  

   shaped, 
  with 
  a 
  median 
  sinus. 
  Surface 
  covered 
  with 
  very 
  numerous 
  

   minute 
  radiations. 
  

  

  Remarks. 
  These 
  specimens 
  appear 
  to 
  agree 
  with 
  the 
  various 
  

   figures 
  of 
  Ch. 
  sarcinulata, 
  5 
  except 
  that 
  they 
  seem 
  less 
  oblong 
  and 
  

   perhaps 
  not 
  quite 
  so 
  transverse, 
  and 
  that 
  the 
  front 
  margin 
  is 
  more 
  

   curved 
  than 
  usually 
  appears 
  in 
  that 
  species. 
  It 
  is, 
  however, 
  quite 
  

   possible 
  that 
  the 
  latter 
  difference 
  may 
  be 
  simply 
  due 
  to 
  crushing 
  

   and 
  flattening. 
  The 
  size 
  of 
  the 
  ribs 
  seems 
  to 
  vary 
  considerably, 
  

   two 
  of 
  the 
  specimens 
  having 
  much 
  coarser 
  ribs 
  and 
  thus 
  approaching 
  

   Ch. 
  plebeia. 
  On 
  the 
  other 
  hand, 
  our 
  typical 
  specimens 
  are 
  quite 
  

   different 
  from 
  the 
  much 
  smaller 
  shells 
  from 
  this 
  quarry 
  above 
  

   referred 
  to 
  Ch. 
  plebeia, 
  and 
  it 
  is 
  possible 
  that 
  these 
  two 
  aberrant 
  

   specimens, 
  which 
  are 
  very 
  indistinct, 
  may 
  belong 
  to 
  neither 
  species 
  

   or 
  not 
  even 
  to 
  the 
  genus 
  Chonetes 
  at 
  all. 
  

  

  1 
  1854. 
  Scbnur, 
  Palreontographica, 
  vol. 
  iii. 
  p. 
  226 
  & 
  pi. 
  xlii. 
  fig. 
  6. 
  

  

  2 
  1883. 
  (Ehlert, 
  Bull. 
  Soc. 
  geol. 
  France, 
  ser. 
  3, 
  vol. 
  xi. 
  p. 
  517 
  & 
  pl.xiv. 
  fig. 
  3. 
  

  

  3 
  1878. 
  Kayser, 
  Abh. 
  geol. 
  Specialk. 
  Preuss. 
  vol. 
  ii. 
  pt. 
  iv. 
  p. 
  200 
  & 
  pis. 
  xxx. 
  

   figs. 
  13, 
  14?, 
  xxxiv. 
  fig. 
  9. 
  

  

  4 
  1889. 
  Kayser, 
  Abh. 
  k. 
  Preuss. 
  geol. 
  Landesanst., 
  n. 
  s., 
  pt. 
  i. 
  p. 
  63 
  & 
  pis. 
  vii. 
  

   figs. 
  2-5, 
  x. 
  fig. 
  7. 
  

  

  5 
  1820. 
  Schlotheim, 
  * 
  Petrefact.' 
  p. 
  256 
  & 
  pi. 
  xxix. 
  fig. 
  3. 
  

  

  