﻿Report 
  of 
  the 
  State 
  Geologist. 
  989 
  

  

  Eumetria, 
  Hall. 
  1863. 
  

   (Plate 
  37, 
  figs. 
  1-12.) 
  

  

  Shells 
  elongate-terebratulif 
  orm 
  ; 
  outline 
  ovate. 
  Yalves 
  sub- 
  

   equally 
  convex. 
  Hinge-line 
  short 
  ; 
  cardinal 
  area 
  of 
  the 
  pedicle- 
  

   valve 
  somewhat 
  elevated, 
  primarily 
  composed 
  of 
  symmetrical 
  

   deltidial 
  plates. 
  In 
  the 
  adult 
  condition 
  the 
  line 
  of 
  symphysis 
  

   between 
  these 
  plates 
  is 
  lost, 
  or 
  represented 
  by 
  a 
  faint 
  line, 
  giv- 
  

   ing 
  the 
  deltarium 
  the 
  appearance 
  of 
  a 
  single 
  vertical, 
  or 
  slightly 
  

   incurved 
  plate, 
  sharply 
  defined 
  on 
  its 
  lateral 
  margins. 
  The 
  

   foramen 
  is 
  apical, 
  its 
  lower 
  side 
  only 
  encroaching 
  on 
  the 
  del- 
  

   tarium. 
  The 
  cardinal 
  extremities 
  are 
  slightly 
  alate, 
  a 
  feature 
  

   more 
  noticeable 
  on 
  the 
  brachial 
  valve 
  and 
  which 
  gives 
  this 
  valve 
  

   a 
  somewhat 
  pectenoid 
  appearance. 
  On 
  the 
  interior 
  of 
  the 
  pedicle- 
  

   valve 
  the 
  teeth 
  are 
  of 
  moderate 
  size, 
  but 
  otherwise 
  the 
  shell 
  is 
  

   nearly 
  devoid 
  of 
  markings 
  of 
  any 
  kind. 
  There 
  is 
  no 
  apical 
  for- 
  

   amina! 
  tube 
  as 
  in 
  Eetzia, 
  no 
  dental 
  lamellae 
  or 
  muscular 
  ridges, 
  

   and 
  only 
  in 
  extremely 
  rare 
  instances 
  is 
  there 
  any 
  trace 
  of 
  the 
  

   muscular 
  impressions. 
  

  

  In 
  the 
  brachial 
  valve 
  the 
  structure 
  of 
  the 
  hinge-plate 
  is 
  very 
  

   complicated. 
  It 
  may 
  be 
  described 
  as 
  composed 
  of 
  two 
  parts, 
  a 
  

   posterior 
  and 
  an 
  anterior. 
  The 
  posterior 
  portion 
  is 
  rather 
  

   broadly 
  crescentic 
  in 
  form, 
  having 
  the 
  curvature 
  of 
  the 
  umbonal 
  

   margin 
  of 
  the 
  valve 
  ; 
  its 
  lateral 
  extensions 
  form 
  the 
  socket-walls, 
  

   which 
  are 
  moderately 
  broad, 
  deep 
  and 
  well 
  defined. 
  On 
  the 
  cen- 
  

   tral 
  portion 
  of 
  this 
  part 
  of 
  the 
  plate 
  rests 
  a 
  second 
  crescent, 
  hav- 
  

   ing- 
  its 
  horns, 
  which 
  make 
  nearlv 
  a 
  semi-circle, 
  directed 
  backward 
  

   and 
  into 
  the 
  umbonal 
  cavity 
  of 
  the 
  opposite 
  valve. 
  At 
  this 
  

   point 
  the 
  curvature 
  of 
  the 
  plate 
  is 
  such 
  that 
  the 
  base 
  of 
  the 
  cres- 
  

   cent 
  lies 
  upon 
  the 
  inner 
  surface 
  of 
  the 
  deltarium 
  of 
  the 
  pedicle- 
  

   valve, 
  its 
  horns 
  crossing 
  the 
  deltarium, 
  extending 
  for 
  fully 
  half 
  

   the 
  length 
  of 
  the 
  umbonal 
  cavity, 
  and 
  being 
  elevated, 
  at 
  their 
  tips, 
  

   above 
  the 
  inner 
  surface 
  of 
  the 
  shell. 
  The 
  posterior 
  part 
  of 
  the 
  

   hinge-plate 
  is 
  connected 
  with 
  the 
  anterior 
  part 
  only 
  by 
  a 
  nar- 
  

   row, 
  thickened 
  median 
  band, 
  which 
  is 
  constricted 
  transversely 
  

   at 
  the 
  point 
  of 
  union, 
  the 
  transverse 
  groove 
  being 
  crossed 
  only 
  

   by 
  a 
  very 
  fine 
  axial 
  ridge. 
  The 
  anterior 
  portion 
  of 
  this 
  plate 
  

   consists 
  of 
  a 
  long, 
  narrow, 
  triangular, 
  concave 
  or 
  spoon-shaped 
  

   central 
  process, 
  the 
  edges 
  of 
  which 
  are 
  sharply 
  elevated, 
  and 
  

   the 
  extremities 
  of 
  these 
  marginal 
  ridges 
  are 
  produced 
  into 
  two 
  

  

  47 
  

  

  