﻿VERTEBRATES. 
  167 
  

  

  and 
  which 
  was 
  originally 
  described 
  as 
  the 
  "third" 
  in 
  the 
  series 
  to 
  

   which 
  the 
  name 
  Cochliodus 
  costatus 
  was 
  given 
  by 
  Messrs. 
  Newberry 
  

   and 
  Worthen. 
  

  

  Viewed 
  from 
  a 
  standpoint 
  taking 
  cognizance 
  of 
  such 
  features 
  as 
  

   they 
  possess 
  in 
  common, 
  the 
  form 
  here 
  alluded 
  to 
  offers 
  marked 
  

   resemblance, 
  in 
  the 
  co-adaptation 
  of 
  the 
  articular 
  borders, 
  to 
  the 
  

   form 
  described 
  by 
  Messrs. 
  Newberry 
  and 
  Worthen 
  as 
  the 
  "second" 
  

   tooth 
  of 
  Cochliodus 
  costatus. 
  Essentially 
  the 
  same 
  contour 
  and 
  reversed 
  

   curvature 
  of 
  the 
  articular 
  borders 
  obtain 
  in 
  the 
  two 
  forms 
  which 
  are 
  

   otherwise 
  unusually 
  like 
  in 
  coronal 
  contour, 
  so 
  much 
  so 
  indeed 
  as 
  

   rather 
  to 
  lead 
  to 
  the 
  conclusion 
  that 
  they 
  are 
  distinct 
  species 
  of 
  the 
  

   same 
  representative 
  form, 
  so 
  little 
  do 
  they 
  differ 
  one 
  from 
  the 
  other 
  

   in 
  outline 
  and 
  contour 
  ; 
  while 
  in 
  Cochliodus 
  the 
  mandibular 
  median 
  

   tooth 
  widely 
  differs 
  in 
  both 
  these 
  respects 
  from 
  the 
  posterior 
  tooth 
  

   with 
  which 
  it 
  was 
  associated. 
  Also, 
  there 
  is 
  an 
  appreciable 
  differ- 
  

   ence 
  in 
  the 
  punctation 
  of 
  the 
  forms 
  here 
  referred 
  to, 
  that 
  of 
  

   "Cochliodus 
  costatus" 
  being 
  coarser 
  and 
  more 
  irregular, 
  and 
  the 
  

   general 
  surface 
  contour 
  more 
  uneven 
  and 
  rugged. 
  

  

  We 
  are 
  at 
  a 
  loss 
  to 
  assign 
  the 
  form 
  here 
  particularly 
  alluded 
  to 
  

   to 
  any 
  of 
  the 
  recognized 
  generic 
  groups. 
  The 
  extreme 
  involution 
  of 
  

   the 
  outer 
  extremity 
  and 
  the 
  obliquity 
  of 
  the 
  postero-lateral 
  border 
  

   do 
  not 
  suggest 
  intimate 
  relations 
  with 
  the 
  median 
  form 
  of 
  Cochli- 
  

   odus 
  ; 
  on 
  the 
  contrary, 
  those 
  features, 
  together 
  with 
  the 
  general 
  out- 
  

   line 
  and 
  conformation 
  of 
  the 
  coronal 
  region, 
  are 
  more 
  consistent 
  

   with 
  the 
  Deltodi, 
  perhaps 
  having 
  closest 
  generic 
  relations 
  with 
  Del- 
  

   todopsis, 
  with 
  the 
  mandibular 
  posterior 
  teeth 
  of 
  which 
  it 
  agrees 
  in 
  

   the 
  obliquity 
  of 
  inrollment, 
  narrow 
  alation, 
  and 
  character 
  of 
  the 
  

   lateral 
  borders. 
  

  

  Geological 
  position 
  and 
  localities: 
  Upper 
  Burlington 
  limestone, 
  

   fish-bed 
  strata 
  ; 
  Burlington, 
  Pleasant 
  Grove, 
  Buffington 
  Creek, 
  Louisa 
  

   Co., 
  Iowa; 
  Quincy, 
  111. 
  

  

  Deltodopsis 
  ? 
  inflexus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XI, 
  Fig. 
  13. 
  

  

  Teeth 
  obliquely 
  trapezoidal 
  in 
  outline, 
  strongly 
  arched 
  and 
  spirally 
  

   inrolled. 
  Lateral 
  borders 
  converging 
  toward 
  outer 
  margin 
  at 
  an 
  

   angle 
  of 
  about 
  25° 
  ; 
  antero-lateral 
  border 
  somewhat 
  obliquely 
  produced 
  

   outward 
  and 
  forward 
  from 
  the 
  obtuse 
  inner 
  angle, 
  character 
  of 
  

   articular 
  edge 
  not 
  known 
  ; 
  postero-lateral 
  or 
  oblique 
  border 
  gently 
  

   arched 
  and 
  more 
  or 
  less 
  sinuous, 
  basal 
  portion 
  greatly 
  thickened 
  

  

  