﻿VERTEBRATES. 
  

  

  227 
  

  

  occurring 
  in 
  the 
  same 
  deposits, 
  it 
  possesses 
  characters 
  of 
  a 
  much 
  

   more 
  intimate 
  nature 
  in 
  common 
  with 
  the 
  same 
  form 
  of 
  P. 
  grandis 
  

   of 
  the 
  Keokuk 
  limestone. 
  But 
  besides 
  its 
  much 
  smaller 
  size, 
  the 
  

   mandibular 
  form 
  departs 
  widely 
  from 
  that 
  of 
  the 
  Keokuk 
  species, 
  as 
  

   will 
  be 
  apparent 
  on 
  comparing 
  the 
  coronal 
  contour 
  of 
  the 
  two 
  spe- 
  

   cies, 
  as 
  shown 
  in 
  the 
  illustrations. 
  The 
  mandibular 
  tooth 
  bears 
  

   some 
  resemblance 
  to 
  the 
  maxillary 
  form 
  of 
  P. 
  angidaris, 
  but 
  besides 
  

   its 
  rugose 
  ornamentation, 
  the 
  punctae 
  exposed 
  in 
  the 
  worn 
  surfaces 
  

   are 
  perceptibly 
  coarser 
  and 
  more 
  crowded 
  than 
  observed 
  in 
  that 
  

   species, 
  which 
  shows 
  a 
  uniformly 
  minutely 
  punctate 
  surface, 
  the 
  

   punctae 
  being 
  rather 
  widely 
  spaced. 
  

  

  Geological 
  position 
  and 
  locality 
  : 
  Chester 
  limestone, 
  Chester, 
  Illinois. 
  

  

  Genus 
  COPODUS, 
  Agassiz. 
  

  

  Copodus, 
  Agassiz, 
  MSS., 
  1859. 
  (Psammodus 
  cornutus, 
  Agass., 
  1838, 
  Poissons 
  Fossiles. 
  

   tome 
  III, 
  p. 
  174; 
  Catalogue 
  of 
  Type 
  Specimens 
  of 
  Fossil 
  Fishes 
  in 
  the 
  Museum 
  of 
  the 
  

   Earl 
  of 
  Enniskillen 
  at 
  Florence 
  Court. 
  Ireland, 
  Geol. 
  Mag. 
  VI, 
  1809; 
  Dr. 
  John 
  J- 
  

   Bigsby, 
  1878; 
  Thesaurus 
  Devonico— 
  Carboniferus; 
  etc. 
  

  

  Teeth 
  bilaterally 
  symmetrical, 
  spanning 
  the 
  jaw 
  

   without 
  mesial 
  suture, 
  arranged 
  in 
  a 
  single 
  longi- 
  

   tudinal 
  series 
  from 
  behind 
  forwards. 
  Lateral 
  bor- 
  

   ders 
  gradually 
  converging 
  anteriorly, 
  where 
  they 
  

   make 
  an 
  obtuse 
  angle 
  with 
  the 
  convex 
  anterior 
  

   margin, 
  posteriorly 
  produced 
  into 
  an 
  acute 
  angle 
  

   meeting 
  the 
  lateral 
  extremities 
  of 
  the 
  concave 
  pos- 
  

   terior 
  margin. 
  Coronal 
  region 
  slightly 
  arched 
  longi- 
  

   tudinally 
  and 
  laterally, 
  distinctly 
  defined 
  from 
  the 
  

   base. 
  The 
  lateral 
  borders 
  of 
  the 
  base 
  form 
  a 
  more 
  

   or 
  less 
  prominent 
  rim 
  projecting 
  beyond 
  the 
  coronal 
  

   limits, 
  beveled 
  or 
  rounded 
  interiorly 
  and 
  more 
  or 
  

   less 
  produced 
  at 
  the 
  postero-lateral 
  angles. 
  The 
  

   anterior 
  and 
  posterior 
  walls 
  vertical 
  to 
  the 
  plane 
  of 
  

   the 
  crown 
  surface 
  and 
  channeled. 
  Inferior 
  surface 
  

   regularly 
  arched 
  transversely, 
  and 
  gently 
  concave 
  

   longitudinally 
  in 
  conformity 
  with 
  the 
  arched 
  coronal 
  contour, 
  the 
  

   tooth 
  attaining 
  maximum 
  depth 
  along 
  the 
  mesial 
  line 
  at 
  the 
  poste- 
  

   rior 
  margin. 
  The 
  crown 
  may 
  present 
  a 
  lunate 
  depression 
  extending 
  

   a 
  greater 
  or 
  less 
  distance 
  backward 
  from 
  the 
  anterior 
  margin 
  and 
  

  

  GENUS 
  COPODUS. 
  

  

  Maxillary 
  form. 
  

  

  Fig. 
  a. 
  Triturating 
  

   surface. 
  

  

  Fig. 
  6. 
  Transverse 
  

   profile 
  from 
  inner 
  

   margin. 
  

  

  Fig. 
  c. 
  Longitudi- 
  

   nal 
  profile. 
  

  

  