﻿146 
  

  

  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIHEEELLID.E. 
  

  

  Fig. 
  2. 
  — 
  Brachial 
  valve 
  of 
  Trimerella 
  grandis. 
  

  

  r, 
  sides, 
  and 
  s, 
  ends 
  of 
  the 
  crescent. 
  

  

  shows 
  something 
  like 
  a 
  hollow 
  that 
  may 
  have 
  been 
  the 
  seat 
  of 
  

   attachment 
  of 
  the 
  umbonal 
  muscle. 
  

  

  Trimerella 
  grandis, 
  chiefly 
  in 
  the 
  form 
  of 
  internal 
  casts, 
  appears 
  

   to 
  be 
  a 
  very 
  abundant 
  fossil 
  in 
  the 
  Guelph 
  limestone 
  — 
  a 
  rock 
  imme- 
  

   diately 
  overlying 
  the 
  Niagara 
  limestone 
  (Upper 
  Silurian), 
  at 
  

   Hespelar, 
  Gait, 
  New 
  Hope, 
  Elora, 
  Guelph, 
  also 
  at 
  Ontario, 
  in 
  

   Canada 
  "West, 
  or 
  about 
  four 
  hundred 
  miles 
  from 
  Montreal. 
  In 
  the 
  

   last 
  locality 
  some 
  specimens 
  have 
  been 
  found 
  three 
  inches 
  and 
  a 
  

   half 
  in 
  length 
  by 
  two 
  in 
  breadth 
  and 
  one 
  in 
  depth. 
  

  

  Teimekeela 
  acuminata, 
  Billings. 
  PI. 
  XV. 
  figs. 
  4-7, 
  and 
  PI. 
  XVI. 
  

   figs. 
  1, 
  2. 
  

  

  Trimerella 
  acuminata, 
  Bill. 
  Memoirs 
  of 
  the 
  Geol. 
  Survey 
  of 
  

   Canada, 
  Paleontology, 
  p. 
  167, 
  fig. 
  151, 
  21 
  Jan. 
  1862. 
  (?) 
  Lind- 
  

   strom, 
  Ofversigt 
  af 
  Kongl. 
  Vet. 
  Akad. 
  Forhandlingar, 
  p. 
  

   253, 
  pi. 
  xxi. 
  "figs. 
  3, 
  4, 
  1867. 
  Ball, 
  American 
  Journ. 
  Conch. 
  

   vol. 
  vii. 
  part 
  2, 
  p. 
  82, 
  1871. 
  Bill. 
  Am. 
  Journ. 
  Sci. 
  Arts, 
  

   3rd 
  ser. 
  p. 
  471, 
  June 
  1871. 
  Billings, 
  Notes 
  on 
  Trimerella 
  

   acuminata, 
  Annals 
  and 
  Mag. 
  of 
  Nat. 
  Hist. 
  4th 
  ser. 
  vol. 
  viii. 
  

   p. 
  140, 
  August 
  1871. 
  Bav. 
  and 
  King, 
  Report 
  of 
  Brighton 
  

   Meeting 
  of 
  Br. 
  Assoc. 
  20 
  August 
  1872. 
  

  

  Shell 
  large 
  ; 
  massive 
  ; 
  longitudinally 
  oval 
  ; 
  broadly 
  rounded 
  in 
  

   front; 
  tapering 
  in 
  its 
  posterior 
  half: 
  surface 
  smooth, 
  or 
  strongly 
  

   marked 
  at 
  intervals 
  by 
  concentric 
  lines 
  of 
  growth. 
  Pedicle-valve 
  mode- 
  

   rately 
  convex 
  : 
  beak 
  produced 
  ; 
  somewhat 
  rounded 
  at 
  its 
  extremity 
  : 
  

   deltidium 
  triangular 
  ; 
  very 
  wide 
  ; 
  deeply 
  concave 
  ; 
  strongly 
  marked 
  

   with 
  anticlinal 
  lines 
  : 
  deltidial 
  ridges 
  well 
  pronounced 
  : 
  areal 
  borders 
  

   narrow 
  : 
  deltidial 
  slope 
  narrow 
  ; 
  marked 
  from 
  side 
  to 
  side 
  by 
  fine 
  

  

  