﻿1863.] 
  

  

  ETHEBIDGE 
  LTASSIC 
  M0LLTJ8CA. 
  

  

  113 
  

  

  the 
  antero-ventral 
  margin. 
  Border 
  angular 
  ; 
  costm 
  concentrically 
  

   arranged, 
  and 
  coincident 
  with 
  the 
  form 
  or 
  contour 
  of 
  the 
  shell. 
  Ven- 
  

   tral 
  margin 
  of 
  each 
  valve 
  strongly 
  denticulate, 
  each 
  having 
  a 
  row 
  of 
  

   strongly 
  defined 
  teeth 
  or 
  serrations, 
  those 
  upon 
  the 
  anterior 
  side 
  being 
  

   most 
  numerous. 
  The 
  teeth 
  occupying 
  the 
  centre 
  of 
  the 
  margin 
  are 
  

   more 
  closely 
  arranged 
  and 
  more 
  deeply 
  set 
  than 
  the 
  lateral 
  ones 
  ; 
  the 
  

   whole 
  are 
  inclined 
  inwards, 
  giving 
  the 
  periphery 
  or 
  edge 
  of 
  the 
  

   shell 
  a 
  bevelled 
  appearance 
  — 
  a 
  marked 
  feature 
  in 
  the 
  shell. 
  

  

  Affinities 
  and 
  Differences. 
  — 
  This 
  remarkable 
  shell 
  somewhat 
  re- 
  

   sembles 
  A. 
  subtetragona 
  from 
  the 
  Upper 
  Lias 
  of 
  Luxembourg, 
  in 
  the 
  

   " 
  Schiste 
  et 
  Marne 
  de 
  Grand-Cour," 
  but 
  its 
  form 
  is 
  more 
  tumid 
  and 
  

   much 
  deeper, 
  the 
  shell 
  is 
  more 
  massive, 
  and 
  the 
  lines 
  of 
  growth 
  are 
  

   not 
  so 
  well 
  defined; 
  and 
  no 
  mention 
  is 
  made 
  in 
  the 
  description 
  of 
  

   that 
  shell 
  of 
  the 
  characteristic 
  and 
  specific 
  character 
  of 
  the 
  dentated 
  

  

  Figs. 
  3-7. 
  — 
  Fossil 
  Shells 
  from 
  the 
  Lias 
  near 
  Belfast. 
  

   Fig. 
  3. 
  Fig. 
  4. 
  

  

  Figs. 
  3 
  & 
  4. 
  — 
  Ceromya 
  gibbosa. 
  Natural 
  size. 
  

   Figs. 
  5 
  to 
  7. 
  — 
  Astarte 
  dentilabrum. 
  Natural 
  size. 
  

  

  edges 
  of 
  the 
  margin 
  of 
  the 
  two 
  valves. 
  It 
  differs 
  from 
  A. 
  ovata 
  of 
  

   the 
  Kimmeridge 
  Clay 
  in 
  its 
  more 
  obtuse 
  umbo 
  and 
  more 
  angular 
  

   lunular 
  ridges; 
  and 
  although 
  A. 
  ovata 
  is 
  strongly 
  dentated 
  along 
  

   the 
  margin, 
  still 
  the 
  dentations 
  are 
  bead-like 
  in 
  the 
  Kimmeridge 
  

   Clay 
  species, 
  and 
  columnar 
  and 
  massive 
  in 
  A. 
  dentilabrum 
  from 
  the 
  

   Lower 
  Lias 
  : 
  both 
  are 
  equally 
  massive 
  in 
  shell-structure. 
  

  

  Dimensions. 
  — 
  Length 
  \^ 
  inch, 
  height 
  T 
  8 
  ^- 
  inch, 
  depth 
  y^ 
  inch. 
  

   vol. 
  xx. 
  — 
  PART 
  I. 
  I 
  

  

  