﻿Report 
  of 
  the 
  State 
  Geologist 
  

  

  1095 
  

  

  and 
  supported 
  by 
  a 
  median 
  septum. 
  In 
  the 
  brachial 
  valve 
  the 
  

   cardinal 
  process 
  is 
  prominent, 
  concave 
  on 
  its 
  inner 
  surface 
  and 
  

   lies 
  in 
  the 
  plane 
  of 
  the 
  valve. 
  The 
  median 
  septum 
  is 
  broad, 
  

   acute 
  at 
  its 
  anterior 
  extremity. 
  Between 
  each 
  of 
  its 
  lateral 
  walls 
  

   and 
  the 
  marginal 
  border 
  of 
  the 
  valve 
  are 
  elongate 
  depressions 
  

   filled 
  with 
  a 
  loose 
  tissue 
  of 
  calcareous 
  spicules. 
  

  

  Figs. 
  653-655. 
  Davidsonella 
  sinuata, 
  Deslongehamps 
  (sp.). 
  (Desloxgchamps.) 
  

  

  Type. 
  Davidsonella 
  sinuata, 
  Deslongchamps 
  (sp.). 
  

   Distribution. 
  Lias. 
  

  

  Lyttonia, 
  Waagen. 
  1883. 
  

  

  Shells 
  of 
  great 
  size, 
  highly 
  inequi 
  valve 
  and 
  very 
  irregular 
  ; 
  fre- 
  

   quently 
  with 
  broad 
  lateral 
  

   expansions. 
  

  

  Pedicle 
  valve 
  convex, 
  thick 
  ; 
  

   apex 
  not 
  distinct 
  ; 
  hinge-line 
  

   short 
  and 
  straight; 
  teeth 
  

   faintly 
  developed. 
  On 
  the 
  

   interior 
  are 
  numerous 
  ridges 
  

   extending 
  in 
  slight 
  curves 
  

   toward 
  the 
  lateral 
  margins 
  ; 
  

   in 
  the 
  median 
  line 
  a 
  smooth 
  

   space 
  bearing 
  a 
  central 
  vertical 
  

   ridge. 
  Brachial 
  valve 
  opercu- 
  

   liform, 
  not 
  extending 
  to 
  the 
  

   margins 
  of 
  the 
  opposite 
  valve. 
  

   Cardinal 
  process 
  small 
  and 
  

   bilobecl 
  ; 
  median 
  surface 
  of 
  the 
  interior 
  with 
  divergent 
  grooves 
  

   corresponding 
  with 
  the 
  ridges 
  of 
  the 
  other 
  valve. 
  

  

  153 
  

  

  Fig. 
  656. 
  

   Lyttonia 
  nobilis, 
  Waagen. 
  

   Fig. 
  656. 
  Cardinal 
  part 
  of 
  a 
  pedicle- 
  valve 
  ; 
  showi- 
  

   ng 
  the 
  hinge-line, 
  median 
  and 
  lateral 
  septa. 
  

   (Waagen.) 
  

  

  