﻿PLATE 
  XXI. 
  

  

  Pholidops 
  oyalis 
  Hall. 
  

  

  Page 
  149. 
  

  

  Figs. 
  I, 
  2. 
  The 
  upper 
  valve 
  and 
  profile 
  view 
  (greatly 
  enlarged) 
  of 
  a 
  specimen 
  

   retaining 
  both 
  valves. 
  

  

  Crania 
  Siluriana 
  Hall. 
  

  

  Page 
  148. 
  

  

  Fig. 
  3. 
  A 
  specimen 
  which 
  retains 
  both 
  valves, 
  attached 
  to 
  the 
  surface 
  of 
  Spirifera. 
  

   Fig. 
  4. 
  The 
  upper 
  valve 
  of 
  a 
  specimen 
  attached 
  to 
  the 
  surface 
  of 
  Platyostoma 
  

  

  Niagarense. 
  Owing 
  to 
  the 
  contour 
  of 
  the 
  surface 
  on 
  which 
  it 
  has 
  

  

  grown, 
  the 
  shell 
  has 
  become 
  elongated 
  and 
  constricted 
  on 
  one 
  side. 
  

   Fig. 
  5. 
  A 
  lateral 
  view 
  of 
  the 
  same, 
  showing 
  the 
  elevation. 
  

   Fig. 
  6. 
  The 
  calyx 
  of 
  Eucalyptocrinus 
  crassus 
  with 
  four 
  ventral 
  valves 
  of 
  the 
  

  

  species 
  attached. 
  

   Fig. 
  7. 
  A 
  specimen 
  of 
  Rhynchonella 
  Stricklandi 
  with 
  a 
  ventral 
  valve 
  of 
  the 
  

  

  species 
  attached. 
  

  

  Crania 
  setifera 
  Hall. 
  

  

  Page 
  148. 
  

  

  Fig. 
  8. 
  A 
  specimen 
  which 
  is 
  imperfect 
  around 
  the 
  margin, 
  but 
  shows 
  the 
  general 
  

   features 
  of 
  the 
  species. 
  

  

  Fig. 
  9. 
  A 
  lateral 
  view 
  of 
  the 
  same, 
  restored 
  on 
  the 
  edge, 
  showing 
  the 
  elevation 
  

  

  of 
  the 
  valve 
  and 
  the 
  position 
  of 
  the 
  apex. 
  

   Fig. 
  10. 
  An 
  enlargement 
  of 
  the 
  surface 
  to 
  show 
  the 
  setiform 
  spines. 
  

  

  Orthis 
  elegantula 
  Dolman. 
  

   Page 
  150. 
  

  

  Figs. 
  11, 
  12. 
  Ventral 
  and 
  dorsal 
  views 
  of 
  a 
  small 
  specimen. 
  

  

  Fig. 
  13. 
  Ventral 
  view 
  of 
  a 
  large 
  individual. 
  

  

  Fig. 
  14. 
  Lateral 
  view 
  of 
  a 
  similar 
  specimen. 
  

  

  Fig. 
  15. 
  Interior 
  of 
  a 
  large 
  ventral 
  valve, 
  showing 
  the 
  cardinal 
  area, 
  teeth 
  and 
  

   wide 
  foramen. 
  

  

  Fig. 
  16. 
  An 
  enlargement 
  to 
  two 
  diameters 
  of 
  the 
  interior 
  of 
  a 
  dorsal 
  valve, 
  show- 
  

   ing 
  the 
  muscular 
  imprints, 
  cardinal 
  and 
  crural 
  processes, 
  and 
  

   external 
  cardinal 
  area. 
  

  

  Fig. 
  17. 
  Cardinal 
  view 
  of 
  the 
  specimen 
  fig. 
  14. 
  

  

  