﻿84 
  PROCEEDINGS 
  OF 
  THE 
  MALACOLOGICAL 
  SOCIETY. 
  

  

  shell 
  ; 
  the 
  surface 
  is 
  also 
  wrinkled, 
  especially 
  posteriorly, 
  caused 
  in 
  

   all 
  probability 
  by 
  a 
  periostracum 
  which 
  must 
  have 
  origiually 
  

   covered 
  the 
  valves 
  as 
  in 
  Raeta. 
  Sometimes 
  the 
  plications 
  are 
  

   irregular, 
  and 
  occasionally 
  they 
  bifurcate 
  midway 
  across 
  the 
  valve, 
  

   terminating 
  singly 
  in 
  the 
  posterior 
  region, 
  when 
  they 
  become 
  more 
  

   distant 
  and 
  consequently 
  fewer. 
  

  

  Smallest 
  example. 
  Largest 
  example. 
  

   Dimensions. 
  

  

  mm. 
  mm. 
  

  

  Length 
  ... 
  25 
  113 
  

  

  Height 
  ... 
  20 
  75 
  

  

  Diameter 
  (closed 
  valves) 
  20 
  60 
  

  

  Distributio7i. 
  — 
  The 
  Upper 
  Lutetian 
  beds 
  of 
  Egypt 
  = 
  Eocene 
  

   formation 
  = 
  Upper 
  Parisian 
  of 
  Europe 
  and 
  the 
  Upper 
  

   Mokattam 
  deposits 
  of 
  Egypt. 
  

   Occurrence. 
  — 
  Cuttings 
  Nos. 
  1, 
  5, 
  6, 
  10. 
  

   Collectors, 
  — 
  Sir 
  Jolm 
  Eaglesome 
  and 
  Dr. 
  Kitson. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  I. 
  

  

  All 
  figures 
  are 
  photographed 
  natural 
  size 
  with 
  the 
  exception 
  of 
  Fig. 
  3, 
  which 
  

  

  is 
  enlarged 
  by 
  about 
  one-fifth. 
  

  

  Raetomya 
  schweinfurthi 
  (Mayer-Eymar). 
  

   Fig. 
  1. 
  — 
  Copy 
  of 
  Mayer-Eymar's 
  original 
  figure 
  of 
  the 
  type 
  from 
  the 
  Eocene 
  

  

  of 
  Egypt. 
  The 
  remaining 
  figures 
  represent 
  specimens 
  from 
  

  

  Southern 
  Nigeria. 
  

   ,, 
  2. 
  — 
  Left 
  lateral 
  view 
  of 
  a 
  pair 
  of 
  closed 
  valves 
  of 
  medium 
  size. 
  

   ,, 
  3. 
  — 
  Dorsal 
  view 
  of 
  same 
  specimen 
  showing 
  the 
  depresso-concave 
  anterior 
  

  

  end, 
  the 
  laterally 
  approximate 
  umbones, 
  and 
  the 
  posterior 
  gape. 
  

  

  Enlarged 
  one-fifth. 
  

   ,, 
  4. 
  — 
  Eight 
  lateral 
  aspect 
  of 
  specimen 
  consisting 
  of 
  a 
  pair 
  of 
  valves 
  of 
  larger 
  

  

  size 
  than 
  Fig. 
  2, 
  showing 
  good 
  testiferous 
  structure 
  and 
  the 
  

  

  bifurcation 
  of 
  the 
  costae 
  in 
  the 
  central 
  part 
  of 
  the 
  shell. 
  

   ,, 
  5. 
  — 
  Dorsal 
  portion 
  of 
  an 
  adult 
  example 
  exhibiting 
  the 
  separation 
  of 
  the 
  

  

  umbones. 
  Note 
  that 
  the 
  right-hand 
  side 
  of 
  this 
  figure 
  is 
  posterior. 
  

   ,, 
  6. 
  — 
  Hinge 
  aspect 
  of 
  the 
  smallest 
  example 
  found, 
  representing 
  a 
  left 
  valve 
  

  

  with 
  the 
  outwardly 
  projecting 
  chondrophore. 
  

   ,, 
  7. 
  — 
  A 
  disconnected 
  hinge 
  region 
  of 
  a 
  left 
  valve 
  belonging 
  to 
  a 
  moderately 
  

  

  large 
  specimen, 
  showing 
  the 
  triangular 
  chondrophore 
  plate 
  with 
  the 
  

  

  long 
  funnel-shaped 
  cavity 
  in 
  front, 
  which 
  is 
  supposed 
  to 
  have 
  held 
  

  

  the 
  anterior 
  portion 
  of 
  the 
  resilium. 
  The 
  black 
  bases 
  of 
  Figs. 
  7 
  

  

  and 
  8 
  represent 
  the 
  hard 
  flinty 
  matrix 
  which 
  fills 
  the 
  remainder 
  of 
  

  

  the 
  valves. 
  

   ,, 
  8. 
  — 
  The 
  opposing 
  hinge 
  of 
  same 
  specimen, 
  showing 
  a 
  differently 
  con- 
  

   stituted 
  chondrophore, 
  and 
  which 
  is 
  vertically 
  disposed 
  in 
  the 
  

  

  sub-umbonal 
  cavity. 
  

   ,, 
  9. 
  — 
  The 
  upper 
  surface 
  of 
  an 
  isolated 
  chondrophore 
  plate, 
  showing 
  its 
  

  

  coalescent 
  elements, 
  and 
  which 
  must 
  have 
  belonged 
  to 
  a 
  very 
  large 
  

  

  example. 
  

   ,, 
  10. 
  — 
  Basal 
  surface 
  of 
  same 
  specimen, 
  more 
  or 
  less 
  bulbous 
  and 
  furrowed, 
  

  

  and 
  quite 
  smooth. 
  

   ,, 
  11. 
  — 
  Portion 
  of 
  a 
  large 
  internal 
  cast 
  with 
  united 
  valves, 
  showing 
  the 
  

  

  postero-lateral 
  surface 
  of 
  the 
  left 
  valve 
  with 
  its 
  extensive 
  and 
  

  

  rounded 
  pallial 
  sinus. 
  

  

  