﻿Report 
  of 
  ihe 
  State 
  Geologist, 
  953 
  

  

  The 
  character 
  of 
  the 
  muscular 
  impressions 
  is 
  of 
  greater 
  impor- 
  

   tance; 
  the 
  broad 
  scars 
  of 
  the 
  diductors* 
  in 
  the 
  pedicle- 
  valve 
  

   are 
  here 
  reduced 
  to 
  very 
  narrow 
  dimensions, 
  are 
  scarcely 
  

   depressed 
  and 
  frequently 
  not 
  defined, 
  but 
  represented 
  only 
  by 
  a 
  

   radiate 
  marking 
  of 
  the 
  shell. 
  In 
  the 
  brachial 
  valve 
  the 
  adductor 
  

   scars 
  are 
  two 
  narrow 
  impressions 
  which 
  widen 
  anteriorly 
  but 
  are 
  

   not 
  divided 
  transversely. 
  The 
  surface 
  of 
  the 
  shell 
  was 
  covered 
  

   with 
  very 
  fine 
  concentric 
  lines 
  and 
  the 
  epidermal 
  layer, 
  which 
  is 
  

   usually 
  effaced, 
  was 
  minutely 
  punctate. 
  Faint 
  lateral 
  plications 
  

   are 
  sometimes 
  visible 
  

  

  These 
  differences 
  from 
  the 
  normal 
  type 
  of 
  Spirifer 
  have 
  led 
  

   many 
  writers 
  to 
  adopt 
  McCoy's 
  term 
  Martiuia 
  for 
  S. 
  glaber 
  and 
  

   its 
  allies. 
  It 
  is 
  evident, 
  however, 
  that 
  this 
  division 
  of 
  the 
  smooth- 
  

   shelled 
  species 
  embraces 
  more 
  than 
  one 
  subordinate 
  type 
  of 
  

   structure 
  ; 
  they 
  may 
  be 
  divided 
  into 
  

  

  1. 
  Aseptati 
  (=Martinia, 
  McCoy, 
  1844). 
  Shells 
  in 
  which 
  dental 
  

   lamellae 
  and 
  septa 
  are 
  wanting. 
  

  

  (S. 
  Maia, 
  Billings, 
  Corniferous 
  limestone 
  ; 
  S. 
  subumbona. 
  Hall, 
  

   Hamilton 
  group 
  ; 
  S. 
  glaber, 
  Martin, 
  Coal 
  Measures.) 
  

  

  2. 
  Sejptati. 
  Shells 
  in 
  which 
  dental 
  plates 
  or 
  septa 
  are 
  well 
  

   developed. 
  Two 
  groups 
  of 
  the 
  septate 
  Glabrati 
  may 
  be 
  recognized 
  : 
  

  

  (a) 
  Martiniopsts, 
  Waagen, 
  1883. 
  Species 
  with 
  the 
  lamellae 
  

   developed 
  in 
  both 
  valves. 
  

  

  ( 
  M. 
  imfiata 
  and 
  M. 
  subpentagonalis, 
  Waagen, 
  from 
  the 
  Productus 
  

   limestone 
  of 
  India). 
  

  

  (b) 
  (" 
  Gen. 
  nov.," 
  Tschernyschew, 
  = 
  Mentzelia, 
  Quenstedt, 
  

   1871(?)), 
  Type 
  of 
  Martinia 
  semiplana, 
  Waagen. 
  Shells 
  with 
  dental 
  

   lamellae 
  scarcely 
  developed, 
  but 
  with 
  a 
  prominent 
  median 
  septum 
  

   in 
  pedicle-valve. 
  Mentzelia 
  was 
  founded 
  upon 
  the 
  Spirifer 
  

   medicmus 
  of 
  the 
  Muschelkalk. 
  

  

  Subgenus 
  Cyrtia, 
  Dalman. 
  1828. 
  

   (Plate 
  29, 
  figs. 
  4-11.) 
  

  

  Shells 
  like 
  Spirieer 
  but 
  having 
  a 
  high 
  vertical 
  cardinal 
  area 
  

   and 
  semi-pyramidal 
  contour. 
  

  

  (Type, 
  C. 
  exporrecta, 
  Wahlenberg. 
  Silurian-Devonian.) 
  

   Cyrtia 
  is 
  the 
  designation 
  of 
  a 
  group, 
  having 
  a 
  meager 
  repre- 
  

   sentation 
  and 
  slight 
  morphological 
  value. 
  

   120 
  11 
  

  

  