﻿154 
  Twenty-eighth 
  Report 
  ox 
  the 
  State 
  Museum. 
  

  

  The 
  species 
  at 
  present 
  known 
  to 
  me 
  as 
  possessing 
  the 
  char- 
  

   acters 
  of 
  the 
  genus 
  are 
  the 
  following 
  : 
  

  

  Sirophonella 
  semifasciata, 
  Niagara 
  group 
  ; 
  Strophonella 
  

   Leavenworthana, 
  S. 
  cavumbona 
  and 
  S. 
  punctulifera 
  (the 
  

   two 
  latter 
  probably 
  identical), 
  Lower 
  Helderberg 
  group 
  ; 
  S. 
  

   ampla, 
  Upper 
  Helderberg 
  group 
  ; 
  S. 
  reversa, 
  Hamilton 
  group, 
  

   Iowa 
  ; 
  S. 
  ccelata, 
  Chemung 
  group. 
  

  

  Strophonella 
  semifasciata. 
  

  

  Plate 
  22, 
  Figs. 
  1-3: 
  PI. 
  23, 
  Figs. 
  7, 
  8. 
  

  

  Strophomena 
  (Strophodonta 
  f) 
  semifasciata 
  Hall. 
  Trans. 
  Alb. 
  lust., 
  vol. 
  iv, 
  p. 
  

  

  210. 
  Abstract, 
  p. 
  16; 
  May, 
  1863. 
  

   Strophomena 
  {Strophodonta 
  ) 
  semifasciata 
  Hall. 
  Doc. 
  Edit. 
  28th 
  Rep. 
  St. 
  Mus. 
  

  

  Nat. 
  Hist. 
  Explanation 
  of 
  plates 
  22 
  and 
  23. 
  1876. 
  

  

  Shell 
  large, 
  concavo-convex, 
  resupinate, 
  transversely 
  semi- 
  

   circular, 
  width 
  nearly 
  twice 
  the 
  length 
  ; 
  cardinal 
  extremities 
  

   somewhat 
  rounded. 
  Ventral 
  valve 
  with 
  slightly 
  elevated 
  

   umbo 
  and 
  small 
  pointed 
  beak 
  ; 
  the 
  middle 
  of 
  the 
  shell 
  deeply 
  

   concave 
  and 
  abruptly 
  inflected 
  toward 
  the 
  front 
  ; 
  area 
  nar- 
  

   row, 
  with 
  a 
  distinct 
  triangular 
  callosity. 
  Dorsal 
  valve 
  de- 
  

   pressed-convex 
  from 
  the 
  umbo 
  to 
  near 
  the 
  middle, 
  becoming 
  

   subgeniculate 
  in 
  front 
  ; 
  area 
  about 
  half 
  as 
  high 
  as 
  that 
  of 
  the 
  

   ventral 
  valve. 
  Both 
  areas 
  distinctly 
  striate, 
  and 
  marked 
  by 
  

   crenulations 
  of 
  the 
  inner 
  margin. 
  

  

  Surface 
  of 
  the 
  upper 
  and 
  middle 
  portions 
  of 
  the 
  shell, 
  

   marked 
  by 
  strong, 
  irregular, 
  distant, 
  rounded, 
  elevated 
  striae 
  ; 
  

   near 
  the 
  front 
  of 
  the 
  shell 
  the 
  striae 
  become 
  more 
  crowded 
  by 
  

   the 
  intercalation 
  of 
  finer 
  ones. 
  Entire 
  surface 
  marked 
  by 
  fine 
  

   concentric 
  striae. 
  Interior 
  surface 
  of 
  valves 
  marked 
  by 
  closely 
  

   set 
  pustules. 
  Substance 
  of 
  shell 
  very 
  thin. 
  

  

  This 
  species 
  has 
  some 
  resemblance 
  to 
  Strophomena 
  euglypha 
  

   (Dalman), 
  but 
  is 
  much 
  more 
  extended 
  on 
  the 
  hinge-line, 
  the 
  

   length 
  and 
  breadth 
  being 
  as 
  two 
  to 
  three 
  ; 
  while 
  in 
  that 
  species 
  

   the 
  proportions 
  are 
  nearly 
  as 
  three 
  to 
  four. 
  This 
  shell 
  has 
  

   not 
  the 
  fine 
  intermediate 
  striae, 
  nor 
  the 
  punctate 
  surface 
  rep- 
  

   resented 
  in 
  that 
  species. 
  It 
  is 
  quite 
  rare, 
  but 
  few 
  specimens 
  

   having 
  been 
  obtained 
  in 
  the 
  entire 
  collection. 
  

  

  