﻿PLATE 
  XXI 
  — 
  (Continued). 
  

  

  Orthis 
  hybrida 
  Soiverly. 
  

  

  Page 
  149. 
  

  

  Fig. 
  18. 
  Dorsal 
  view 
  of 
  a 
  specimen 
  of 
  the 
  usual 
  form 
  and 
  size. 
  

  

  Fig. 
  19. 
  Ventral 
  view 
  of 
  the 
  same. 
  

  

  Fig. 
  20. 
  Dorsal 
  view 
  of 
  an 
  unusually 
  large 
  specimen. 
  

  

  Fig. 
  21. 
  Lateral 
  view 
  of 
  the 
  specimen 
  figures 
  18 
  and 
  19, 
  showing 
  the 
  relative 
  

   convexity 
  of 
  the 
  valves. 
  

  

  Fig. 
  22. 
  The 
  interior 
  of 
  a 
  dorsal 
  valve, 
  showing 
  the 
  muscular 
  impression, 
  cardi- 
  

   nal 
  process, 
  etc. 
  

  

  Fig. 
  23. 
  The 
  interior 
  of 
  a 
  ventral 
  valve, 
  showing 
  muscular 
  imprints, 
  teeth, 
  etc. 
  

   The 
  shell 
  is 
  slightly 
  distorted 
  and 
  imperfect 
  on 
  the 
  cardinal 
  margin. 
  

  

  Figs. 
  24, 
  25. 
  Dorsal 
  and 
  lateral 
  views 
  of 
  a 
  small 
  rotund 
  specimen, 
  showing 
  strong 
  

   varices 
  of 
  growth 
  ; 
  enlarged 
  to 
  two 
  diameters. 
  

  

  Streptorhynchus 
  subplaina 
  (Conrad). 
  

  

  Page 
  151. 
  

  

  Fig. 
  26. 
  The 
  interior 
  of 
  a 
  dorsal 
  valve, 
  showing 
  the 
  cardinal 
  process, 
  etc. 
  

  

  Fig. 
  27. 
  An 
  imperfect 
  ventral 
  valve, 
  showing 
  muscular 
  imprints, 
  teeth 
  and 
  cardi- 
  

   nal 
  area. 
  

  

  Fig. 
  28. 
  Dorsal 
  view 
  of 
  a 
  symmetrical 
  specimen 
  of 
  the 
  larger 
  size. 
  

  

  Figs. 
  29, 
  30. 
  Ventral 
  and 
  dorsal 
  views 
  of 
  a 
  specimen 
  of 
  the 
  asual 
  size 
  of 
  the 
  

   species 
  as 
  it 
  occurs 
  at 
  Waldron. 
  

  

  Fig. 
  31. 
  Ventral 
  view 
  of 
  the 
  same, 
  showing 
  the 
  convexity 
  of 
  the 
  valves. 
  

  

  Fig. 
  32. 
  An 
  enlargement 
  of 
  the 
  surface, 
  showing 
  the 
  fine 
  concentric 
  striae. 
  

  

  Fig. 
  33. 
  An 
  enlargement 
  of 
  the 
  central 
  part 
  of 
  the 
  cardinal 
  area 
  of 
  the 
  united 
  

   valves, 
  showing 
  the 
  closed 
  deltidium, 
  the 
  striae, 
  etc. 
  

  

  