﻿112 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [DeC. 
  2, 
  

  

  Descriptions 
  of 
  New 
  Species 
  of 
  Mollusca, 
  Src. 
  

   By 
  R. 
  Etheridge, 
  Esq., 
  F.G.S., 
  F.R.S.E. 
  

  

  Ceromya 
  gibbosa, 
  Etheridge. 
  

  

  Shell 
  ventricose, 
  deep, 
  especially 
  at 
  the 
  umbonal 
  region, 
  or 
  above 
  the 
  

   position 
  of 
  the 
  oral 
  and 
  anal 
  adductors. 
  Umbones 
  small, 
  nearly 
  

   central 
  or 
  subterminal, 
  slightly 
  curved 
  or 
  involute, 
  leaving 
  a 
  wide 
  

   and 
  exposed 
  lunular 
  region. 
  Anterior 
  side 
  produced, 
  rounded, 
  and 
  

   gaping. 
  Posterior 
  side, 
  during 
  life, 
  apparently 
  closed, 
  attenuated, 
  

   slightly 
  truncate. 
  Ventral 
  margin 
  much 
  produced, 
  giving 
  the 
  shell 
  

   a 
  nearly 
  circular 
  appearance. 
  

  

  The 
  umbonal 
  region 
  of 
  this 
  shell 
  is 
  strongly 
  marked 
  by 
  concentric 
  

   ridges 
  or 
  lines 
  of 
  growth, 
  which 
  rapidly 
  disappear 
  with 
  age, 
  and 
  finally 
  

   pass 
  into 
  well-defined 
  but 
  fine 
  or 
  closely 
  arranged 
  concentric 
  striae. 
  

   Beneath 
  the 
  outer 
  shell, 
  which 
  is 
  thin 
  and 
  papyraceous, 
  are 
  longitu- 
  

   dinal 
  or 
  highly 
  inclined 
  slightly 
  impressed 
  ribs 
  ; 
  these 
  are 
  shown 
  on 
  

   the 
  exposed 
  surface 
  of 
  the 
  right 
  valve 
  near 
  the 
  ventral 
  margin. 
  These 
  

   lines, 
  from 
  their 
  direction, 
  do 
  not 
  come 
  directly 
  from 
  the 
  limb, 
  but 
  

   apparently 
  from 
  about 
  the 
  middle 
  of 
  the 
  posterior 
  region 
  of 
  the 
  dorsal 
  

   side 
  or 
  surface. 
  

  

  Dimensions. 
  — 
  Height 
  1^ 
  inch, 
  depth 
  1^ 
  inch, 
  length 
  2^ 
  inches. 
  

  

  Affinities 
  and 
  Differences. 
  — 
  This 
  shell 
  in 
  general 
  outline 
  resembles 
  

   C.latior, 
  Ag., 
  from 
  the 
  Inferior 
  Oolite 
  beds 
  of 
  Longuy 
  (Luxembourg) 
  ; 
  

   but 
  the 
  postero-dorsal 
  margin 
  being 
  much 
  more 
  elevated, 
  and 
  the 
  

   ventral 
  margin 
  much 
  more 
  produced 
  or 
  rounded, 
  indeed 
  nearly 
  

   circular, 
  quite 
  distinguish 
  C. 
  gibbosa 
  from 
  C. 
  latior 
  ; 
  added 
  to 
  this, 
  

   the 
  finely 
  engraved 
  concentric 
  lines 
  on 
  the 
  ventral 
  portion 
  of 
  the 
  outer 
  

   shell, 
  which 
  so 
  rapidly 
  change 
  their 
  character 
  from 
  those 
  of 
  the 
  strongly 
  

   marked 
  and 
  elevated 
  lines 
  of 
  growth 
  near 
  the 
  umbo, 
  distinguish 
  

   it 
  from 
  any 
  known 
  species. 
  The 
  deeper 
  -seated 
  vertical 
  ribs 
  on 
  

   the 
  sides 
  (beneath 
  the 
  outer 
  shell), 
  which 
  appear 
  to 
  be 
  directed 
  

   obliquely 
  or 
  excentrically 
  from 
  the 
  umbones 
  towards 
  the 
  ventral 
  

   margin, 
  although 
  resembling 
  certain 
  species 
  from 
  the 
  Inferior 
  Oolite, 
  

   are 
  nevertheless 
  quite 
  distinct. 
  

  

  On 
  the 
  posterior 
  side 
  of 
  the 
  umbo, 
  near 
  the 
  escutcheon, 
  there 
  is 
  a 
  

   singular 
  growth 
  or 
  expansion 
  of 
  the 
  shell 
  passing 
  from 
  the 
  right 
  valve, 
  

   which 
  overlaps 
  the 
  edges 
  of 
  both 
  valves, 
  quite 
  obliterating 
  the 
  line 
  of 
  

   union 
  over 
  the 
  corselet. 
  This 
  does 
  not 
  appear 
  to 
  be 
  accidental, 
  but 
  

   part 
  of 
  the 
  shell-structure, 
  and 
  is 
  exhibited 
  in 
  the 
  two 
  specimens 
  

   known. 
  

  

  Locality. 
  — 
  Discovered 
  by 
  Mr. 
  William 
  Gray 
  on 
  the 
  east 
  shore 
  of 
  

   Larne 
  Lough. 
  

  

  Astarte 
  dentil 
  abrum, 
  Etheridge.* 
  

  

  /Shell 
  massive, 
  ovate, 
  and 
  deep. 
  Postero 
  -dorsal 
  surface 
  rounded. 
  Pos- 
  

   terior 
  end 
  slightly 
  truncate 
  from 
  about 
  the 
  position 
  of 
  the 
  anal 
  ad- 
  

   ductor 
  to 
  the 
  ventral 
  margin 
  or 
  border. 
  Anterior 
  margin 
  acutely 
  

   rounded. 
  Umbones 
  small, 
  indistinct, 
  subcentral, 
  slightly 
  curved 
  

   anteriorly. 
  Lunule 
  slightly 
  excavated, 
  small, 
  oval, 
  and 
  attenuated, 
  

   occupying 
  half 
  the 
  area 
  between 
  the 
  umbo 
  and 
  the 
  commencement 
  of 
  

  

  