﻿1042 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  Muscular 
  impressions 
  not 
  clearly 
  defined 
  in 
  the 
  pedicle- 
  valve, 
  

   but 
  in 
  the 
  brachial 
  valve 
  are 
  two 
  oblong 
  or 
  subovate 
  scars 
  a 
  little 
  

   below 
  the 
  beak, 
  one 
  on 
  each 
  side 
  of 
  the 
  median 
  line. 
  

  

  Type, 
  Stricklandinia 
  Gaspensis, 
  Billings. 
  

  

  Distribution. 
  Upper 
  Silurian. 
  

  

  Amphigenia, 
  Hall. 
  1867. 
  

   (Plate 
  49, 
  figs. 
  8-15.) 
  

  

  Shells 
  elongate-ovoid, 
  high-shouldered, 
  broadest 
  behind 
  and 
  

   sloping 
  to 
  a 
  narrow 
  curve 
  anteriorly 
  ; 
  without 
  median^ 
  fold 
  and 
  

   sinus. 
  Surface 
  smooth, 
  with 
  irregularly 
  distant 
  concentric 
  

   growth-rings 
  and 
  faint 
  radial 
  striae. 
  There 
  is 
  no 
  cardinal 
  area, 
  

   and 
  deltidial 
  plates 
  are 
  not 
  developed 
  in 
  the 
  large 
  triangular 
  

   delthyrium. 
  In 
  the 
  pedicle-valve 
  is 
  a 
  short 
  spondyiium 
  formed 
  

   by 
  the 
  union 
  of 
  the 
  dental 
  lamellae 
  with 
  the 
  median 
  ^septum. 
  

   The 
  muscles 
  were 
  implanted 
  upon 
  this 
  spondyiium 
  and 
  there 
  is 
  

   no 
  evidence 
  of 
  scars 
  elsewhere 
  upon 
  the 
  valve 
  except 
  those 
  left 
  

   by 
  the 
  vascular 
  sinuses 
  upon 
  the 
  post-lateral 
  surfaces. 
  In 
  the 
  

   brachial 
  valve 
  is 
  a 
  large 
  subquadrate 
  hinge-plate, 
  perforated 
  by 
  

   the 
  visceral 
  foramen 
  which 
  with 
  age 
  becomes 
  filled 
  up 
  by 
  

   adventitious 
  deposits. 
  The 
  crura 
  are 
  long, 
  straight, 
  inclining 
  

   upward 
  or 
  toward 
  the 
  opposite 
  valve 
  and 
  are 
  expanded 
  at 
  their 
  

   extremities 
  into 
  palmate 
  processes. 
  The 
  muscular 
  scars 
  in 
  this 
  

   valve 
  are 
  sharply 
  developed, 
  forming 
  together 
  an 
  elongate 
  

   adductor 
  area, 
  clearly 
  divisible 
  into 
  an 
  attenuate 
  anterior 
  pair 
  

   and 
  a 
  broader 
  posterior 
  pair. 
  The 
  former 
  have 
  about 
  twice 
  the 
  

   length 
  of 
  the 
  latter 
  and 
  are 
  marked 
  by 
  transverse, 
  fine, 
  closely- 
  

   set 
  wrinkles 
  ; 
  the 
  latter 
  are 
  radiately 
  and 
  coarsely 
  striate. 
  From 
  

   the 
  posterior 
  termination 
  of 
  this 
  area 
  to 
  beneath 
  the 
  hinge-plate 
  

   extends 
  a 
  broad, 
  smooth 
  sinus, 
  from 
  which 
  is 
  given 
  off 
  a 
  pair 
  of 
  

   strong 
  lateral 
  branches, 
  which 
  ramify 
  over 
  the 
  genital 
  area 
  in 
  

   the 
  umbonal 
  region. 
  

  

  The 
  substance 
  of 
  the 
  shell 
  is 
  impunctate 
  on 
  the 
  surface. 
  

   Beneath 
  the 
  epidermal 
  layer 
  is 
  another 
  that 
  is 
  highly 
  punctated 
  ; 
  

   within 
  this, 
  and 
  apparently 
  forming 
  the 
  innermost 
  lamina, 
  is 
  a 
  

   third 
  Layer 
  whose 
  surface 
  is 
  minutely 
  wrinkled. 
  

  

  Type, 
  Amphigenia 
  elongata, 
  Yanuxem 
  (sp.). 
  

  

  Distribution. 
  Lower 
  Devonian 
  (Corniferous 
  limestone). 
  

  

  100 
  

  

  