﻿74 
  ME. 
  F. 
  E. 
  COWPEE 
  EEED 
  ON 
  THE 
  [Feb. 
  1897^ 
  

  

  America, 
  from 
  which 
  it 
  was 
  first 
  described 
  by 
  Hall 
  l 
  under 
  the 
  

   name 
  of 
  Atrypa 
  dentata. 
  Recently 
  it 
  has 
  been 
  assigned 
  by 
  Hall 
  & 
  

   Clarke 
  2 
  to 
  the 
  genus 
  Rhynchotrema. 
  The 
  species 
  much 
  resembles 
  

   Rhynchonella 
  ? 
  cemula 
  (Salter 
  MS.) 
  described 
  by 
  Davidson 
  3 
  from 
  

   the 
  Kildare 
  Limestone, 
  but 
  in 
  this 
  Irish 
  form 
  the 
  mesial 
  fold 
  of 
  the 
  

   brachial 
  valve 
  becomes 
  biplicated 
  only 
  near 
  the 
  front 
  margin 
  of 
  the 
  

   shell, 
  and 
  the 
  two 
  short 
  rounded 
  ribs 
  on 
  each 
  side 
  of 
  it 
  are 
  confined 
  

   to 
  the 
  edges 
  of 
  the 
  valve. 
  In 
  Rh. 
  dentatum, 
  on 
  the 
  other 
  hand, 
  the 
  

   mesial 
  fold 
  is 
  strongly 
  biplicated 
  nearly 
  from 
  the 
  beak, 
  while 
  each 
  

   lateral 
  portion 
  is 
  furnished 
  with 
  three 
  simple, 
  slightly 
  curved 
  ribs, 
  

   extending 
  entirely 
  from 
  the 
  beak 
  to 
  the 
  margin. 
  The 
  ' 
  zigzag 
  

   filiform 
  lines 
  ' 
  which 
  Hall 
  describes 
  in 
  the 
  American 
  individuals 
  

   are 
  also 
  distinguishable 
  on 
  the 
  ribs 
  of 
  our 
  specimen. 
  

  

  The 
  American 
  specimens 
  appear 
  to 
  have 
  rather 
  sharper 
  and 
  more 
  

   angular 
  ribs 
  than 
  the 
  Keisley 
  form. 
  This, 
  however, 
  is 
  the 
  only 
  

   point 
  of 
  difference 
  that 
  I 
  have 
  been 
  able 
  to 
  detect. 
  

  

  Davidson's 
  Rhynchonella 
  decemplicata* 
  from 
  the 
  Bala 
  and 
  Upper 
  

   Llandovery 
  beds, 
  has 
  more 
  numerous 
  ribs 
  on 
  the 
  lateral 
  portions, 
  

   but 
  otherwise, 
  so 
  far 
  as 
  external 
  characters 
  go, 
  much 
  resembles 
  

   Rhynchotrema 
  dentatum. 
  

  

  millim. 
  

  

  Length 
  of 
  shell 
  4 
  

  

  Breadth 
  4 
  

  

  Dayia 
  pentagonalis, 
  sp. 
  n. 
  (PI. 
  VI. 
  figs. 
  5, 
  5 
  a, 
  5 
  b, 
  & 
  5 
  c.) 
  

  

  Shell 
  subpentagonal, 
  broadest 
  across 
  the 
  middle, 
  biconvex. 
  

   Hinge-line 
  curved. 
  No 
  hinge-area. 
  Pedicle-valve 
  more 
  convex 
  than 
  

   the 
  brachial 
  valve, 
  especially 
  near 
  the 
  beak 
  ; 
  beak 
  closely 
  curved 
  

   over 
  the 
  hinge-line, 
  concealing 
  foramen. 
  Beak 
  of 
  pedicle-valve 
  

   furnished 
  with 
  a 
  longitudinal, 
  broad, 
  rounded 
  keel 
  ; 
  at 
  about 
  one- 
  

   third 
  the 
  length 
  of 
  the 
  valve 
  a 
  shallow 
  median 
  furrow 
  begins 
  on 
  

   this 
  keel 
  or 
  ridge, 
  and 
  extends 
  to 
  the 
  front 
  margin, 
  increasing 
  in 
  

   width 
  anteriorly 
  and 
  thus 
  making 
  a 
  double 
  keel 
  on 
  the 
  anterior 
  

   portion 
  of 
  the 
  valve. 
  The 
  lateral 
  portions 
  of 
  the 
  valve 
  on 
  the 
  slopes 
  

   of 
  the 
  median 
  keel 
  are 
  slightly 
  excavated, 
  and 
  are 
  bounded 
  posteriorly 
  

   on 
  each 
  side 
  by 
  a 
  small 
  narrow 
  fold 
  starting 
  from 
  the 
  side 
  of 
  the 
  

   beak 
  and 
  curving 
  round 
  in 
  its 
  outward 
  course 
  to 
  the 
  end 
  of 
  the 
  

   hinge-line, 
  so 
  as 
  to 
  give 
  the 
  appearance 
  of 
  a 
  false 
  hinge- 
  area 
  

   between 
  it 
  and 
  the 
  hinge-line, 
  as 
  in 
  some 
  Rhynchonellids. 
  

  

  The 
  brachial 
  valve 
  is 
  more 
  convex 
  posteriorly 
  than 
  towards 
  the 
  

   front 
  margin. 
  A 
  shallow 
  groove 
  begins 
  close 
  in 
  front 
  of 
  the 
  umbo, 
  

   and 
  extends 
  forward, 
  with 
  a 
  steadily 
  increasing 
  width 
  and 
  depth, 
  

   to 
  the 
  anterior 
  edge 
  of 
  the 
  shell, 
  where 
  it 
  has 
  a 
  smooth 
  flattened 
  

   floor 
  with 
  low, 
  steep, 
  and 
  abrupt 
  sides. 
  The 
  lateral 
  portions 
  of 
  this 
  

   valve 
  are 
  gently 
  convex. 
  

  

  The 
  anterior 
  margin 
  of 
  the 
  shell 
  is 
  broadly 
  notched, 
  owing 
  to 
  the 
  

   meeting 
  of 
  the 
  median 
  sinuses 
  of 
  the 
  opposite 
  valves. 
  In 
  the 
  

   umbonal 
  cavity 
  of 
  the 
  pedicle-valve 
  are 
  seen 
  two 
  short, 
  divergent, 
  

  

  1 
  ' 
  Pal. 
  N. 
  Y.,' 
  vol. 
  i. 
  (1847) 
  p. 
  148, 
  pi. 
  xxxiii. 
  fig. 
  14. 
  

  

  2 
  Ibid. 
  vol. 
  viii, 
  Brach. 
  pt. 
  ii. 
  (1894) 
  p. 
  182. 
  

  

  3 
  'Mon. 
  Brit. 
  Foss. 
  Brach.,' 
  vol. 
  iii. 
  (1864-71) 
  p. 
  188, 
  pi. 
  xxiv. 
  fig. 
  21. 
  

  

  4 
  Ibid. 
  p. 
  177, 
  pi. 
  xxiii. 
  figs. 
  20-24. 
  

  

  