﻿Report 
  of 
  the 
  State 
  Geologist, 
  961 
  

  

  as 
  in 
  Merista, 
  but 
  as 
  a 
  rule 
  the 
  ribbon 
  makes 
  fewer 
  (from 
  six 
  to 
  

   twelve) 
  volutions 
  at 
  maturity. 
  The 
  jugum 
  is 
  simple, 
  the 
  branches 
  

   being 
  more 
  nearly 
  erect 
  than 
  in 
  Merista, 
  Meristella, 
  etc., 
  and 
  

  

  Figs. 
  302, 
  303.— 
  The 
  jugum 
  of 
  Whitfieldella 
  nitida, 
  Hall. 
  

  

  beyond 
  their 
  junction 
  continued 
  into 
  a 
  short, 
  acute, 
  generally 
  

   slightly 
  curved 
  process, 
  which 
  makes 
  a 
  large 
  angle 
  with 
  the 
  

   direction 
  of 
  the 
  lateral 
  branches. 
  The 
  muscular 
  impressions, 
  

   which 
  are 
  very 
  faint, 
  are 
  divided, 
  longitudinally, 
  by 
  the 
  median 
  

   septum, 
  and 
  transversely, 
  into 
  anterior 
  and 
  posterior 
  scars. 
  

   From 
  the 
  ante-lateral 
  margins 
  of 
  the 
  muscular 
  area 
  in 
  both 
  valves 
  

   radiates 
  a 
  series 
  of 
  vascular 
  sinuses, 
  the 
  principal 
  trunks 
  of 
  which 
  

   are 
  very 
  conspicuous 
  ; 
  this 
  feature, 
  however, 
  is 
  rarely 
  retained. 
  

   External 
  surface 
  of 
  the 
  valves 
  smooth 
  or 
  concentrically 
  striate. 
  

   Shell-substance 
  fibrous, 
  impunctate. 
  

  

  Type, 
  Whitfieldella 
  nitida, 
  Hall, 
  (sp.). 
  Niagara 
  group. 
  

  

  Distribution. 
  Upper 
  Silurian 
  — 
  Lower 
  Devonian. 
  

  

  Hyattella, 
  Hall. 
  1893. 
  

  

  (Plate 
  32, 
  figs. 
  10-17.) 
  

  

  Shell 
  compactly 
  subpentahedral; 
  the 
  umbo 
  of 
  the 
  pedicle- 
  valve 
  

   acute, 
  concealing 
  most 
  of 
  the 
  deltidial 
  covering. 
  The 
  pedicle- 
  

   valve 
  bears 
  a 
  strong 
  median 
  sinus 
  and 
  two 
  

   faint 
  lateral 
  sinuses, 
  the 
  opposite 
  valve 
  

   having 
  corresponding 
  folds. 
  The 
  surface 
  

   of 
  the 
  shell 
  and 
  the 
  ante-lateral 
  margins 
  

   are 
  deeply 
  sinuate. 
  Fine, 
  sharp, 
  closely 
  _ 
  M 
  _ 
  _ 
  „ 
  mn 
  

  

  rj 
  J 
  r? 
  J 
  fxg. 
  £04.— 
  The 
  loop 
  of 
  Hyatt- 
  

  

  crowded 
  concentric 
  striae 
  cover 
  the 
  exterior, 
  eiia 
  congesta, 
  Conrad. 
  

   The 
  interior 
  of 
  the 
  pedicle-valve 
  has 
  a 
  deep 
  and 
  strongly 
  striate 
  

   pedicle-cavity, 
  bounded 
  by 
  strong 
  dental 
  lamellae 
  ; 
  the 
  diductor 
  

   scars 
  are 
  distinctly 
  defined, 
  inclosing 
  a 
  linear 
  adductor. 
  In 
  the 
  

   brachial-valve 
  the 
  hinge 
  plate 
  is 
  triangular 
  and 
  divided 
  medially 
  

   by 
  a 
  deep 
  cleft. 
  The 
  lateral 
  portions 
  are 
  broad 
  and 
  elevated, 
  

   121 
  19 
  

  

  