﻿The 
  Fauna 
  of 
  the 
  Niagara 
  Group. 
  151 
  

  

  Streptorhynchus 
  subplana 
  {Conrad). 
  

  

  Plate 
  21, 
  Figs. 
  26-33. 
  

  

  Strophomen 
  a 
  subplana 
  Conrad. 
  Journ. 
  Acad. 
  Nat. 
  Soc. 
  Phil., 
  vol. 
  viii, 
  p. 
  258. 
  1842. 
  

  

  Leptcena 
  subplana 
  (Conr.) 
  Hall,. 
  Pal. 
  1ST. 
  Y., 
  vol. 
  ii, 
  p. 
  259, 
  pi. 
  53, 
  figs. 
  8-10. 
  1852. 
  

  

  Streptorhynchus 
  subplana 
  (Conr.) 
  Hall. 
  Trans. 
  Alb. 
  Inst., 
  vol. 
  iv, 
  p. 
  226. 
  Ab- 
  

   stract, 
  p. 
  32; 
  May, 
  1863. 
  16th 
  Rep. 
  State 
  Cab. 
  Nat. 
  Hist., 
  p. 
  63. 
  Geol. 
  Rep. 
  Wis. 
  

   1862, 
  p. 
  436. 
  

  

  This 
  species 
  occurs 
  somewhat 
  abundantly, 
  and 
  differs 
  but 
  

   slightly 
  from 
  the 
  New 
  York 
  form. 
  It 
  is 
  proportionally 
  wider 
  

   and 
  shows 
  less 
  of 
  the 
  tendency 
  to 
  become 
  mucronate 
  at 
  the 
  

   cardinal 
  angles. 
  

  

  STROPHOMENA 
  Raf. 
  

   Strophomena 
  rhomboldalis 
  Wilckens. 
  

  

  Plate 
  22, 
  Figs. 
  4-10. 
  

  

  Conchites 
  rhomboidalis 
  Wilckens. 
  Nachricht 
  von 
  seltener 
  Verst, 
  p. 
  77, 
  pi. 
  viii, 
  

  

  figs. 
  43, 
  44. 
  1769. 
  

   For 
  Synonymy, 
  see 
  Pal. 
  N. 
  Y., 
  vol. 
  iii, 
  p. 
  195, 
  under 
  Strophomena 
  rugosa 
  ; 
  and 
  

   ibid. 
  vol. 
  iv, 
  p. 
  76. 
  

  

  This 
  variable 
  species 
  is 
  very 
  abundant, 
  and 
  occurs 
  of 
  some- 
  

   what 
  larger 
  size 
  than 
  those 
  figured. 
  Specimens 
  having 
  a 
  width 
  

   of 
  50 
  mm. 
  are 
  not 
  uncommon. 
  

  

  STROPHODONTA 
  Hall. 
  

   Strophodonta 
  profunda. 
  

  

  Plate 
  23, 
  Figs. 
  9, 
  10. 
  

  

  Leptcena 
  profunda 
  Hall. 
  Pal. 
  N. 
  Y., 
  vol. 
  ii, 
  p. 
  61, 
  pi. 
  21, 
  figs. 
  4, 
  5. 
  1852. 
  

   Strophodonta 
  profunda 
  Hall. 
  20th 
  Report 
  State 
  Cab. 
  Nat. 
  Hist., 
  p. 
  369, 
  pi. 
  13, 
  

   figs. 
  3, 
  4. 
  1867. 
  Revised 
  Ed., 
  p. 
  376, 
  pi. 
  13, 
  figs. 
  3, 
  4. 
  [1870.] 
  

  

  Shell 
  large, 
  broadly 
  semioval, 
  the 
  full 
  grown 
  individuals 
  

   having 
  a 
  width 
  of 
  about 
  60 
  mm. 
  with 
  a 
  length 
  of 
  about 
  40 
  

   mm. 
  ; 
  greatest 
  width 
  along 
  the 
  hinge-line 
  ; 
  deeply 
  concavo- 
  

   convex, 
  point 
  of 
  greatest 
  convexity 
  in 
  front 
  of 
  the 
  middle. 
  

   Cardinal 
  angles 
  slightly 
  extended 
  and 
  subauriculate, 
  in 
  the 
  

   casts 
  often 
  obtuse 
  or 
  rounded. 
  

  

  Ventral 
  valve 
  very 
  convex, 
  beak 
  slightly 
  elevated, 
  cardinal 
  

   margin 
  sloping 
  and 
  a 
  little 
  concave 
  to 
  the 
  cardinal 
  angles, 
  

  

  