﻿The 
  Fauxa 
  of 
  the 
  Niagara 
  Group. 
  179 
  

  

  CEPHALOPODA. 
  

  

  ORTHOCERAS 
  Breyn. 
  

   Grthoceras 
  simulator. 
  

  

  Plate 
  27, 
  Figs. 
  11, 
  12. 
  

  

  Orthoceras 
  simulator 
  Hai/l. 
  Doc. 
  Edit. 
  28th 
  Rep. 
  St. 
  Mus. 
  Nat. 
  Hist. 
  Explana- 
  

   tion 
  of 
  pi. 
  27, 
  figs. 
  11, 
  12. 
  1876. 
  

  

  Shell 
  cylindrical, 
  gradually 
  enlarging, 
  siphuncle 
  subcentral; 
  

   septa 
  distant 
  from 
  each 
  other 
  about 
  one-fourth 
  »of 
  the 
  dia- 
  

   meter 
  of 
  the 
  shell 
  — 
  from 
  three 
  to 
  four 
  in 
  the 
  space 
  of 
  14 
  

   millimetres. 
  

  

  Surface 
  finely 
  striated 
  transversely. 
  

  

  The 
  diameter 
  of 
  the 
  largest 
  specimen 
  observed 
  is 
  25 
  milli- 
  

   metres. 
  

  

  The 
  specimens 
  are 
  frequently 
  flattened 
  and 
  in 
  very 
  bad 
  con- 
  

   dition, 
  the 
  shell 
  being 
  entirely 
  destroyed, 
  and 
  usually 
  the 
  

   septa 
  are 
  obliterated. 
  

  

  TROCHOCERAS 
  Barrande 
  Hall. 
  

   Trochoceras 
  Waldronense. 
  

  

  Plate 
  27, 
  Figs. 
  13-15. 
  

  

  Trochoceras 
  Waldronensis 
  Hai/l. 
  Doc. 
  Edit. 
  28th 
  Rep. 
  St. 
  Mus. 
  Nat. 
  Hist. 
  Ex- 
  

   planation 
  of 
  pi. 
  27, 
  figs. 
  13-15. 
  1876. 
  

  

  Shell 
  dextral, 
  making 
  about 
  two 
  volutions 
  ; 
  spire 
  depressed, 
  

   volutions 
  slightly 
  flattened 
  ; 
  section 
  subelliptical 
  ; 
  gradually 
  

   expanding, 
  and 
  the 
  outer 
  chamber 
  continued 
  in 
  a 
  more 
  direct 
  

   line 
  ; 
  siphuncle 
  excentric, 
  nearer 
  to 
  the 
  concave 
  dorsal 
  margin 
  ; 
  

   septa 
  moderately 
  convex. 
  

  

  Surface 
  marked 
  by 
  strong 
  annulations, 
  which 
  are 
  oblique 
  

   and 
  abruptly 
  curved 
  backward 
  on 
  the 
  convexo-ventral 
  side, 
  

   very 
  gradually 
  increasing 
  in 
  distance 
  from 
  each 
  other, 
  to 
  the 
  

  

  