﻿296 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  thirds 
  down 
  the 
  shell. 
  The 
  opposite 
  valve 
  has 
  the 
  strong, 
  tokened, 
  

   and 
  slightly 
  divergent 
  lamellae 
  characteristic 
  of 
  Spinfer, 
  a 
  nign 
  but 
  

   narrow 
  cardinal 
  area 
  (fig. 
  12), 
  above 
  which 
  the 
  thick 
  convex 
  beak 
  is 
  

  

  slightly 
  incurved. 
  . 
  

  

  We 
  have 
  a 
  variety 
  in 
  which 
  the 
  sinus 
  is 
  not 
  only 
  depressed 
  more 
  

   than 
  usual, 
  but 
  has 
  a 
  furrow 
  down 
  its 
  middle. 
  

  

  8. 
  SrnnEE*DAviDis,Rouault? 
  PI. 
  XVII. 
  fig. 
  13. 
  Renault, 
  Bull. 
  

   Soc. 
  Geol. 
  Fr. 
  2nd 
  ser. 
  vol. 
  viii. 
  p. 
  368. 
  

  

  The 
  shape 
  agrees 
  with 
  that 
  of 
  M. 
  Renault's 
  shell, 
  which 
  however 
  

   has 
  fewer 
  ribs— 
  only 
  thirty-six 
  in 
  all. 
  

  

  These 
  are 
  the 
  oldest-known 
  species 
  of 
  the 
  genus 
  ; 
  if 
  indeed 
  it 
  

   be 
  not 
  the 
  case 
  that 
  they 
  are, 
  as 
  above 
  suggested, 
  pebbles 
  from 
  some 
  

   Devonian 
  rock, 
  mixed 
  with 
  the 
  others. 
  

  

  9. 
  Lept^na 
  Vicaryi, 
  spec. 
  nov. 
  PI. 
  XVII. 
  figs. 
  16, 
  17. 
  

  

  Nearly 
  nine 
  lines 
  long 
  by 
  eleven 
  wide, 
  and 
  with 
  a 
  depth 
  of 
  five 
  

   Hues. 
  The 
  larger 
  valve 
  of 
  this 
  species 
  presents 
  a 
  highly 
  inflated 
  iorm, 
  

   gibbous 
  in 
  fact, 
  for 
  the 
  convexity 
  is 
  greatest 
  above 
  the 
  middle 
  of 
  the 
  

   shell 
  The 
  beak 
  is 
  very 
  prominent 
  and 
  projecting 
  in 
  iront^ 
  ana 
  

   rather 
  compressed 
  than 
  broad. 
  There 
  is 
  a 
  very 
  slight 
  central 
  sinus, 
  

   but 
  no 
  fold 
  in 
  front, 
  the 
  shell 
  being 
  quite 
  regularly 
  convex 
  through- 
  

   out. 
  The 
  hinge-line 
  is 
  just 
  equal 
  to 
  the 
  width, 
  the 
  ears 
  square, 
  and 
  

   the 
  front 
  angles 
  rounded 
  off. 
  

  

  We 
  have 
  only 
  one 
  (internal) 
  cast 
  of 
  the 
  larger 
  valve. 
  It 
  shows 
  

   deep 
  radiate 
  muscular 
  scars 
  near 
  the 
  beak, 
  on 
  each 
  side, 
  and 
  is 
  

  

  vxccjj 
  i»^"" 
  ^ 
  + 
  fxthax 
  miss 
  ^oto 
  ova 
  +wo 
  oxternal 
  

  

  ? 
  .^§ 
  w 
  ^&^jy,°^nicn 
  snow 
  it 
  to 
  nave 
  oeen 
  regularly 
  but 
  not 
  so 
  deeply 
  

   concave 
  as 
  the 
  other, 
  with 
  a 
  few 
  concentric 
  wavy 
  lines 
  of 
  growth, 
  

   becoming 
  rather 
  strong 
  rugae 
  along 
  the 
  hinge-line. 
  These 
  ridges 
  

   decussate 
  the 
  margin 
  roughly, 
  and 
  become 
  grouped 
  in 
  pairs 
  or 
  threes, 
  

   mixed 
  too 
  with 
  frequent 
  short 
  longitudinal 
  depressions, 
  which 
  give 
  

   the 
  idea 
  of 
  bases 
  of 
  spines, 
  and 
  which 
  are 
  scattered 
  all 
  over 
  the 
  sur- 
  

   face 
  (probably 
  of 
  both 
  valves). 
  The 
  central 
  line 
  is 
  concave 
  in 
  a 
  

   narrowed 
  area 
  (as 
  the 
  other 
  valve 
  is 
  convex 
  along 
  the 
  median 
  space), 
  

   and 
  there 
  is 
  a 
  depressed 
  line 
  answering 
  to 
  the 
  median 
  plate 
  within. 
  

   Faint 
  radii 
  occur 
  on 
  the 
  surface 
  of 
  both 
  valves. 
  

  

  I 
  know 
  no 
  Silurian 
  species, 
  except 
  the 
  small 
  L. 
  quadrata 
  of 
  Russia 
  

   and 
  L. 
  tenuicincta 
  of 
  Britain, 
  which 
  resembles 
  this 
  in 
  form. 
  Both 
  

   are 
  much 
  smaller 
  and 
  less 
  gibbous. 
  

  

  10. 
  Rhtnchonella, 
  sp. 
  PI. 
  XVII. 
  fig. 
  15. 
  

  

  This 
  is 
  certainly 
  not 
  the 
  Terebratida 
  Thebeaultii, 
  Rouault, 
  from 
  

   Gahard, 
  Rennes 
  ; 
  and 
  I 
  know 
  no 
  other 
  French 
  form 
  to 
  compare 
  with 
  

   it. 
  It 
  is 
  not 
  unlike 
  several 
  of 
  our 
  British 
  Caradoc 
  forms, 
  and 
  is 
  not 
  

   worth 
  a 
  separate 
  description. 
  It, 
  too, 
  may 
  possibly 
  be 
  a 
  Devonian 
  

   fossil 
  introduced 
  into 
  these 
  beds 
  : 
  M. 
  de 
  Verneuil 
  thinks 
  it 
  very 
  

   like 
  jR. 
  Pareti, 
  a 
  common 
  Devonian 
  fossil 
  in 
  W. 
  Europe. 
  It 
  has 
  

   thin, 
  subparallel, 
  short 
  cardinal 
  lamellae. 
  

  

  