﻿APPENDIX. 
  

  

  DESCRIPTION 
  OF 
  SHELL 
  FOUND 
  IN 
  THE 
  JAMES 
  RIVER 
  AT 
  HURON, 
  

  

  S. 
  DAK., 
  JULY 
  27, 
  1913. 
  

  

  (Fig. 
  1, 
  2, 
  and 
  3, 
  pi. 
  I.) 
  

  

  Form 
  of 
  shell. 
  — 
  Subtriangular, 
  the 
  anterior 
  margin 
  forming 
  the 
  rounded 
  apex 
  of 
  the 
  

   elongated 
  triangle, 
  the 
  posterior 
  margin 
  forming 
  the 
  base; 
  dorsal 
  margin 
  nearly 
  straight; 
  

   ventral 
  margin 
  about 
  equal 
  in 
  length 
  to 
  dorsal 
  but 
  slightly 
  curved. 
  Much 
  inflated; 
  

   the 
  umbones 
  high, 
  arched, 
  and 
  nearly 
  meeting; 
  umbones 
  situated 
  well 
  forward, 
  one- 
  

   third 
  of 
  distance 
  from 
  anterior 
  margin. 
  Greatest 
  inflation 
  in 
  region 
  of 
  umbonal 
  slope. 
  

  

  Sculpture. 
  — 
  A 
  pronounced 
  ridge 
  extends 
  along 
  posterior 
  border 
  of 
  umbones 
  to 
  

   postero- 
  ventral 
  angle 
  of 
  shell; 
  the 
  anterior 
  border 
  of 
  the 
  ridge 
  is 
  somewhat 
  roughened; 
  

   a 
  slight 
  but 
  distinct 
  furrow 
  limits 
  the 
  posterior 
  border 
  of 
  the 
  ridge. 
  Just 
  beneath 
  each 
  

   of 
  the 
  four 
  upper 
  concentric 
  color 
  rings 
  are 
  pronounced 
  ridges 
  hi 
  the 
  anterior 
  portion 
  

   of 
  the 
  shell. 
  Rest-markings 
  consist 
  of 
  three 
  or 
  four 
  short 
  concentric 
  ridges, 
  very 
  dis- 
  

   tinct 
  but 
  thin 
  and 
  close 
  together. 
  

  

  Color. 
  — 
  -Generally 
  brownish 
  straw-color; 
  greenish 
  in 
  highest 
  part 
  of 
  umbones, 
  yel- 
  

   lowish 
  anteriorly 
  and 
  ventrally, 
  dark 
  brownish 
  in 
  posterior 
  portion. 
  The 
  specimen 
  

   in 
  hand 
  shows 
  six 
  distinct 
  dark 
  concentric 
  rings 
  — 
  the 
  so-called 
  "rest" 
  or 
  "growth" 
  

   rings. 
  

  

  Internal 
  aspect. 
  — 
  Shell 
  cavity 
  very 
  deep; 
  umbonal 
  cavity 
  deep; 
  the 
  shell 
  relatively 
  

   thin; 
  nacre 
  lustrous 
  white 
  anteriorly, 
  iridescent 
  bluish 
  orviolet 
  in 
  thin 
  posterior 
  third. 
  

   Cardinal 
  teeth 
  double 
  in 
  both 
  valves, 
  but 
  compressed 
  and 
  relatively 
  weak, 
  especially 
  

   so 
  in 
  right 
  valve 
  ; 
  anterior 
  much 
  stronger 
  than 
  posterior 
  in 
  left 
  valve; 
  anterior 
  somewhat 
  

   stronger 
  than 
  posterior 
  in 
  right 
  valve. 
  Lateral 
  teeth 
  long, 
  compressed, 
  blade-like, 
  

   elevated, 
  slightly 
  curved, 
  double 
  in 
  left, 
  single 
  in 
  right 
  valve; 
  lateral 
  teeth 
  scarcely 
  

   continuous 
  with 
  cardinal 
  teeth; 
  hinge 
  plate 
  above 
  lateral 
  teeth 
  practically 
  wanting. 
  

   Anterior 
  retractor 
  impression 
  sejxirate 
  from 
  anterior 
  adductor, 
  both 
  roughened; 
  pos- 
  

   terior 
  adductor 
  impression 
  smooth; 
  pallial 
  line 
  not 
  conspicuous, 
  broad 
  and 
  faintly 
  

   striate 
  in 
  anterior 
  half; 
  dorsal 
  muscle 
  scars 
  scarcely 
  visible. 
  

  

  Characteristic 
  features 
  of 
  the 
  shell 
  are 
  its 
  triangular 
  or 
  pyramidal 
  

   form 
  and 
  its 
  remarkable 
  inflation, 
  which 
  are 
  strongly 
  suggestive 
  of 
  

   the 
  mflated 
  types 
  of 
  L. 
  luteola; 
  its 
  compressed 
  sharp 
  teeth, 
  which 
  are 
  

   of 
  the 
  Lam'psilis 
  type 
  to 
  an 
  extreme 
  ; 
  the 
  color 
  of 
  epidermis 
  and 
  char- 
  

   acter 
  and 
  color 
  of 
  nacre, 
  which 
  find 
  correspondence 
  only 
  in 
  species 
  of 
  

   Quadrula, 
  especially 
  in 
  Quadrula 
  undulata. 
  The 
  pyramidal 
  shape 
  of 
  

   the 
  shell 
  is 
  also 
  suggestive 
  of 
  Q. 
  undulata. 
  It 
  is 
  not 
  possible 
  at 
  the 
  

   present 
  time 
  to 
  place 
  the 
  specimen 
  in 
  any 
  described 
  genus. 
  

  

  17 
  

  

  