﻿Report 
  of 
  the 
  State 
  Geologist. 
  

  

  1079 
  

  

  Subgenus 
  Eudesia, 
  King. 
  1850. 
  

  

  Synonym 
  ; 
  Fldbelloihyris, 
  Deslongchamps, 
  1884. 
  

   Biconvex 
  shells, 
  with 
  dental 
  plates, 
  median 
  dorsal 
  septum, 
  long 
  

   recurved 
  loop 
  and 
  sharply 
  plicated 
  exterior. 
  

  

  Figs. 
  579, 
  580. 
  Eudesia 
  cardium, 
  Lamarck 
  (sp.) 
  (DouvillA.) 
  

  

  (Type, 
  Eudesia 
  cardium, 
  Lamarck 
  (sp.). 
  Jurassic.) 
  

  

  Subgenus 
  Orthotoma, 
  Quenstedt. 
  1871. 
  

  

  Shells 
  small, 
  subcircular, 
  biconvex, 
  smooth, 
  with 
  marginal 
  

   median 
  sinus 
  on 
  the 
  brachial 
  valve. 
  Hinge-line 
  straight. 
  

  

  Figs. 
  581, 
  588. 
  Orthotoma 
  Heyseana, 
  Dunker 
  (sp.). 
  (Quknstedt.) 
  

  

  (Type, 
  Orthotoma 
  Heyseana, 
  Dunker 
  (sp.). 
  Jurassic.) 
  

  

  Subgenus 
  Aulacothyris, 
  Douville. 
  1880. 
  

  

  Shells 
  smooth, 
  naviculoid 
  in 
  contour 
  ; 
  brachial 
  valve 
  with 
  a 
  

   broad 
  median 
  sinus, 
  pedicle-valve 
  with 
  conspicuous 
  median 
  ridge. 
  

   Dental 
  plates 
  and 
  dorsal 
  median 
  septum 
  well 
  developed. 
  Loop 
  

   long, 
  fimbriate. 
  

  

  137 
  

  

  