﻿VERTEBRATES. 
  145 
  

  

  Deltodus 
  latior, 
  St. 
  J, 
  and 
  W. 
  

  

  PI. 
  IX, 
  Pig. 
  11-12. 
  

  

  Mandibular 
  posterior 
  teeth 
  moderately 
  arched 
  longitudinally 
  and 
  

   rather 
  strongly 
  inrolled, 
  in 
  general 
  outline 
  and 
  dimensions 
  resemb- 
  

   ling 
  the 
  same 
  form 
  of 
  Deltodus 
  occidentalis 
  with 
  which 
  they 
  are 
  

   associated. 
  Antero-lateral 
  border 
  slightly 
  incurved, 
  in 
  length 
  exceeded 
  

   by 
  the 
  breadth 
  across 
  the 
  inner 
  margin, 
  enamel 
  fold 
  defined 
  from 
  

   the 
  basal 
  border 
  by 
  a 
  shallow 
  groove 
  ; 
  general 
  course 
  of 
  inner 
  margin 
  

   slightly 
  oblique 
  to 
  the 
  anterior 
  border, 
  broadly 
  arched 
  round 
  the 
  

   base 
  of 
  the 
  coronal 
  prominence 
  with 
  a 
  slight 
  concavity 
  between 
  the 
  

   median 
  and 
  the 
  posterior 
  angles 
  ; 
  postero-lateral 
  border 
  gradually 
  

   converging 
  toward 
  the 
  outer 
  margin- 
  The 
  upper 
  edge 
  defined 
  by 
  a 
  

   rather 
  thick 
  fold 
  of 
  the 
  coronal 
  enamel. 
  Coronal 
  ridge 
  most 
  prom- 
  

   inent 
  in 
  the 
  middle 
  portion 
  of 
  its 
  extent, 
  depressed 
  near 
  the 
  inner 
  

   margin, 
  culminating 
  in 
  an 
  obtusely 
  rounded 
  crest 
  a 
  little 
  anterior 
  

   of 
  the 
  median 
  line, 
  anterior 
  slope 
  flat 
  or 
  slightly 
  depressed, 
  pos- 
  

   teriorly 
  steeply 
  inclined 
  into 
  the 
  depression 
  on 
  that 
  side, 
  which 
  is 
  

   bordered 
  by 
  the 
  rather 
  wide 
  moderately 
  upraised 
  alate 
  expansion. 
  

   Surface 
  punctation 
  very 
  like 
  that 
  observed 
  in 
  D. 
  occidentalis. 
  Length 
  

   of 
  a 
  medium 
  size 
  tooth 
  along 
  the 
  antero-lateral 
  border 
  to 
  inrolled 
  

   outer 
  margin 
  15 
  mm. 
  ; 
  breadth 
  across 
  inner 
  margin 
  19 
  mm. 
  

  

  The 
  posterior 
  form 
  of 
  the 
  mandible 
  alone 
  is 
  known, 
  of 
  which 
  the 
  

   collections 
  contain 
  but 
  few 
  examples. 
  These 
  present, 
  in 
  the 
  contour 
  

   of 
  the 
  crown 
  and 
  proportions 
  of 
  the 
  coronal 
  prominence 
  and 
  alate 
  

   lobe, 
  characters 
  which 
  certainly 
  offer 
  striking 
  contrast 
  to 
  those 
  prev- 
  

   alent 
  in 
  Deltodus 
  occidentalis, 
  with 
  whose 
  remains 
  they 
  are 
  asso- 
  

   ciated. 
  The 
  same 
  observations 
  are 
  equally 
  admissible 
  when 
  com- 
  

   pared 
  with 
  the 
  same 
  form 
  of 
  D. 
  undulatus, 
  N. 
  and 
  W., 
  also 
  of 
  

   the 
  Keokuk, 
  and 
  D. 
  spatulatus, 
  N. 
  and 
  W., 
  of 
  the 
  Upper 
  Burlington 
  

   •limestone. 
  In 
  the 
  depressed 
  anterior 
  slope 
  and 
  the 
  consequent 
  

   greater 
  or 
  less 
  prominence 
  of 
  the 
  coronal 
  ridge, 
  these 
  teeth 
  bear 
  

   some 
  resemblance 
  to 
  the 
  homologous 
  form 
  of 
  Cochliodus; 
  however, 
  

   the 
  condition 
  of 
  the 
  coronal 
  fold 
  of 
  the 
  antero-lateral 
  border 
  as 
  also 
  

   the 
  coronal 
  contour 
  leave 
  no 
  room 
  for 
  doubt 
  as 
  to 
  their 
  congeneric 
  

   relations 
  with 
  Deltodus. 
  The 
  paucity 
  of 
  examples 
  and 
  the 
  absence 
  

   of 
  identifiable 
  individuals 
  of 
  the 
  opposite 
  jaw 
  have 
  occasioned 
  much 
  

   hesitation 
  in 
  recognizing 
  the 
  specific 
  distinctness 
  of 
  the 
  teeth 
  here 
  

   alluded 
  to; 
  the 
  materials 
  illustrating 
  D. 
  spatulatus, 
  D. 
  occidentalis, 
  

  

  —10 
  

  

  