﻿VERTEBRATES. 
  231 
  

  

  line 
  of 
  the 
  anterior 
  margin. 
  Inferior 
  surface 
  moderately 
  concave 
  

   longitudinally, 
  and 
  quite 
  strongly 
  arched 
  transversely, 
  meeting 
  at 
  

   the 
  median 
  line 
  in 
  an 
  obtuse 
  angle, 
  the 
  dense 
  surface 
  layer 
  longi- 
  

   tudinally 
  striated. 
  Transverse 
  diameter 
  across 
  posterior 
  margin 
  at 
  

   least 
  22 
  mm. 
  ; 
  length 
  along 
  the 
  median 
  line 
  probably 
  12 
  mm. 
  ; 
  

   greatest 
  depth 
  of 
  tooth 
  6 
  mm. 
  

  

  The 
  form 
  first 
  mentioned 
  above, 
  and 
  which 
  is 
  regarded 
  as 
  hav- 
  

   ing 
  belonged 
  to 
  the 
  upper 
  jaw, 
  presents 
  as 
  typical 
  an 
  example 
  of 
  

   the 
  genus, 
  as 
  does 
  Copodus 
  cornutus 
  of 
  Agassiz. 
  It 
  is 
  distinguished 
  

   from 
  that 
  form 
  by 
  the 
  more 
  regularly 
  arched 
  outline 
  of 
  the 
  anterior 
  

   margin 
  and 
  the 
  transverse 
  convexity 
  of 
  the 
  crown- 
  surface, 
  in 
  the 
  

   latter 
  respect 
  bearing 
  greater 
  resemblance 
  to 
  C. 
  spatulatus, 
  Agass., 
  

   from 
  which, 
  however, 
  it 
  is 
  distinguishable 
  by 
  the 
  more 
  constant 
  pos- 
  

   terior 
  expansion 
  of 
  the 
  borders 
  of 
  the 
  crown 
  proper. 
  

  

  The 
  form 
  pertaining 
  to 
  the 
  mandible 
  bears 
  a 
  striking 
  resemblance 
  

   to 
  the 
  teeth 
  designated 
  under 
  the 
  generic 
  term 
  Labodus, 
  Agass., 
  and 
  

   which 
  may 
  well 
  be 
  supposed 
  to 
  be 
  homologous 
  with 
  the 
  present 
  

   form. 
  It 
  differs 
  markedly 
  from 
  the 
  typical 
  species 
  indicated 
  by 
  

   Professor 
  Agassiz, 
  L. 
  prototypus, 
  from 
  the 
  Irish 
  Mountain 
  limestone, 
  

   in 
  the 
  relatively 
  great 
  transverse 
  convexity 
  of 
  the 
  coronal 
  surface. 
  

  

  The 
  discovery 
  of 
  the 
  above 
  species 
  adds 
  another 
  name 
  to 
  the 
  

   long 
  list 
  of 
  genera 
  common 
  to 
  the 
  Lower 
  Carboniferous 
  formations 
  

   of 
  the 
  Old 
  and 
  New 
  Worlds. 
  The 
  specific 
  designation 
  is 
  given 
  in 
  

   honor 
  of 
  W. 
  C. 
  Van 
  Home, 
  Esq. 
  

  

  Geological 
  position 
  and 
  localities 
  : 
  St. 
  Louis 
  limestone 
  ; 
  St. 
  Louis, 
  

   Mo., 
  and 
  Alton, 
  111. 
  

  

  Copodus 
  pusillus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XX, 
  Fig. 
  1. 
  

  

  Teeth 
  very 
  small.' 
  Form 
  pertaining 
  to 
  the 
  upper 
  jaw 
  subrhom- 
  

   boidal 
  in 
  outline, 
  lateral 
  borders 
  very 
  gradually 
  converging 
  and 
  

   somewhat 
  sharply 
  rounded 
  into 
  the 
  slightly 
  arched 
  anterior 
  margin, 
  

   the 
  worn 
  tooth 
  showing 
  the 
  posterior 
  margin 
  also 
  broadly 
  arched 
  

   backward. 
  The 
  coronal 
  region 
  is 
  gently 
  and 
  about 
  equally 
  arched 
  

   in 
  both 
  directions, 
  with 
  a 
  faint 
  narrow 
  depression 
  near 
  the 
  lateral 
  

   borders, 
  which 
  latter 
  are 
  bordered 
  by 
  ,a 
  narrow 
  fold 
  beveled 
  to 
  and 
  

   distinctly 
  defined 
  from 
  the 
  basal 
  rim; 
  in 
  front 
  the 
  coronal 
  belt 
  

   forms 
  a 
  narrow 
  lenticular 
  strip 
  inbeveled 
  to 
  the 
  channeled 
  basal 
  

   wall, 
  and 
  above 
  the 
  usual 
  lunate 
  triturating 
  area. 
  The 
  coronal 
  

   surface 
  was 
  enveloped 
  in 
  a 
  dense 
  enamel 
  layer 
  marked 
  by 
  faint 
  

  

  