﻿846 
  Forty- 
  seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  times 
  broadly 
  grooved 
  median 
  fold, 
  with 
  regular 
  and 
  even 
  lateral 
  

   slopes. 
  In 
  the 
  interior 
  of 
  the 
  valves 
  the 
  form 
  of 
  the 
  muscular 
  

   scars 
  is 
  normal, 
  though 
  there 
  is 
  a 
  notable 
  variation 
  in 
  the 
  size 
  of 
  

   the 
  diductor 
  scars. 
  

  

  St. 
  Louis 
  group. 
  Washington 
  county, 
  Indiana; 
  Colesburgh 
  y 
  

   Kentucky. 
  

  

  Seminula 
  Dawsoni, 
  sp. 
  nov. 
  

  

  (Plate 
  xlvii, 
  figs. 
  32-34.) 
  

   (See 
  pages 
  95, 
  96.) 
  

  

  This 
  species 
  was 
  originally 
  identified 
  as 
  Athyris 
  subtilita 
  Hall, 
  

   by 
  Davidson 
  (Quarterly 
  Journal 
  of 
  the 
  Geological 
  Society 
  of 
  

   London, 
  vol. 
  XIX, 
  J 
  8ti3). 
  Its 
  differences 
  from 
  this 
  species 
  are 
  

   indicated 
  on 
  the 
  pages 
  referred 
  to. 
  

  

  Carboniferous 
  limestone. 
  Windsor, 
  Nova 
  Scotia. 
  

  

  Meristella 
  Walcotti, 
  sp. 
  nov. 
  

  

  (Plates 
  xliii, 
  figs. 
  16, 
  17; 
  xliv, 
  figs. 
  6-11, 
  23, 
  32.) 
  

   Shell 
  elongate 
  ovate, 
  valves 
  convex, 
  regular. 
  Pedicle-valve 
  

   with 
  umbo 
  moderately 
  full 
  and 
  beak 
  incurved 
  ; 
  foramen 
  generally 
  

   concealed 
  at 
  maturity. 
  Cardinal 
  slopes 
  concave 
  and 
  well 
  delimi- 
  

   ted 
  by 
  divergent 
  cardinal 
  ridges. 
  Dorsum 
  more 
  or 
  less 
  distinctly 
  

   ridged 
  in 
  the 
  umbonal 
  region, 
  broadly 
  convex 
  anteriorly 
  and 
  

   slightly 
  extended 
  on 
  the 
  anterior 
  margin 
  but 
  with 
  no 
  median 
  

   sinus. 
  Brachial 
  valve 
  with 
  the 
  median 
  elevation 
  somewhat 
  more 
  

   strongly 
  defined, 
  especially 
  in 
  the 
  umbonal 
  region. 
  Umbo- 
  

   lateral 
  slopes 
  rather 
  more 
  abrupt 
  than 
  in 
  the 
  other 
  valve. 
  

   Internal 
  structure 
  normal 
  for 
  the 
  genus. 
  

   Oriskany 
  sandstone. 
  Cayuga, 
  Ontario. 
  

  

  Merista 
  Tennesseensis, 
  sp. 
  nov. 
  

   (Plate 
  xlii, 
  figs. 
  1-6.) 
  

  

  Shell 
  subpentahedral 
  in 
  outline, 
  tran 
  verse, 
  rarely 
  elongate. 
  

   Valves 
  subequally 
  convex, 
  with 
  broad, 
  low 
  fold 
  and 
  sinus 
  

   developed 
  on 
  the 
  anterior 
  portion 
  of 
  the 
  brachial 
  and 
  pedicle- 
  

   valves 
  respectively. 
  Umbo 
  of 
  pedicle-valve 
  not 
  conspicuous, 
  apex 
  

   truncated 
  at 
  maturity 
  by 
  a 
  circular 
  foramen. 
  Deltidial 
  plates 
  

   concealed 
  by 
  incurvature. 
  Umbo 
  of 
  brachial 
  valve 
  full, 
  apex 
  

   acute. 
  External 
  surface 
  smooth. 
  Dimensions 
  of 
  an 
  average 
  

   example: 
  length, 
  17 
  mm.; 
  greatest 
  width, 
  19 
  mm. 
  

  

  Upper 
  Silurian. 
  Perry 
  county, 
  Tennessee. 
  

  

  