﻿VEKTEBKATES. 
  169 
  

  

  lateral 
  border, 
  from 
  which 
  it 
  is 
  separated 
  by 
  a 
  relatively 
  narrow 
  

   intervening 
  depression, 
  which 
  is 
  bordered 
  on 
  the 
  one 
  hand 
  by 
  the 
  low, 
  

   narrow 
  alation, 
  and 
  on 
  the 
  other 
  by 
  the 
  abrupt 
  posterior 
  slope 
  of 
  the 
  

   coronal 
  ridge, 
  the 
  wide 
  anterior 
  slope 
  descending 
  with 
  gentle 
  con- 
  

   cavity 
  to 
  the 
  narrow 
  raised 
  fold 
  along 
  the 
  antero-lateral 
  border. 
  

   Surface 
  regularly 
  marked 
  by 
  strong. 
  transverse 
  ridges 
  or 
  undulations 
  

   spaced 
  by 
  narrow 
  grooves 
  parallel 
  with 
  the 
  inner 
  margin, 
  and 
  

   enveloped 
  in 
  a 
  dense 
  enamel 
  layer, 
  the 
  worn 
  areas 
  showing 
  coarse^ 
  

   widely-spaced 
  punctse. 
  Transverse 
  diameter 
  across 
  the 
  inner 
  margin 
  

   about 
  8 
  mm. 
  ; 
  length 
  of 
  antero-lateral 
  border 
  to 
  ^oint 
  of 
  inrollment, 
  "p/ 
  

   about 
  4 
  mm. 
  

  

  The 
  form 
  above 
  noticed 
  is 
  represented 
  in 
  the 
  collection 
  of 
  Mr. 
  

   Yan 
  Home 
  by 
  a 
  single 
  specimen, 
  the 
  postero-lateral 
  border 
  of 
  which 
  

   is 
  broken 
  away, 
  so 
  that 
  the 
  entire 
  outline 
  of 
  the 
  tooth 
  is 
  not 
  shown.. 
  

   In 
  general 
  outline 
  and 
  coronal 
  contour, 
  it 
  bears 
  intimate 
  resemblance 
  

   to 
  a 
  congeneric 
  form 
  of 
  the 
  Upper 
  Burlington, 
  Deltodopsis 
  (?) 
  convo- 
  

   lutus; 
  it 
  may, 
  however, 
  be 
  distinguished 
  from 
  that 
  form 
  by 
  the 
  

   greater 
  obliquity 
  of 
  the 
  anterior 
  portion 
  of 
  the 
  inner 
  margin, 
  the 
  

   probable 
  greater 
  width 
  and 
  more 
  distinct 
  definition 
  of 
  the 
  posterior 
  

   alate 
  lobe, 
  and 
  the 
  strong 
  transverse 
  undulations 
  of 
  the 
  crown 
  to 
  

   which 
  it 
  owes 
  its 
  ornate 
  character. 
  

  

  Geological 
  position 
  and 
  locality: 
  Warsaw 
  limestone 
  ; 
  -eerite- 
  of 
  Piasa 
  ■mou?**' 
  

   creek, 
  above 
  Alton, 
  Illinois. 
  

  

  Deltodopsis 
  ? 
  btalveatus, 
  D. 
  ? 
  Keokuk, 
  and 
  D. 
  ? 
  convexus. 
  

  

  PI. 
  XI, 
  Fig. 
  15-18. 
  

  

  Teeth 
  wedge-shaped 
  viewed 
  from 
  above, 
  moderately 
  arched 
  in 
  the 
  

   direction 
  of 
  inrollment. 
  Lateral 
  borders 
  deep, 
  very 
  gradually 
  con- 
  

   verging 
  from 
  within 
  outward 
  with 
  a 
  slightly 
  oblique 
  course; 
  basal 
  

   portion 
  proportionately 
  very 
  deep, 
  channeled 
  above, 
  with 
  a 
  wide 
  

   slightly 
  inbeveled 
  belt 
  below, 
  terminating 
  in 
  a 
  more 
  or 
  less 
  sharply 
  

   rounded 
  rim 
  defining 
  the 
  excavated 
  and 
  sometimes 
  longitudinally 
  

   furrowed 
  inferior 
  surface, 
  defined 
  above 
  by 
  the 
  relatively 
  narrow, 
  

   rounded, 
  inbeveled 
  enamel 
  fold 
  ; 
  inner 
  margin 
  obliquely 
  and 
  gently 
  

   rounded 
  from 
  the 
  obtuse 
  anterior 
  ( 
  ?) 
  angle 
  to 
  the 
  subacute 
  angle 
  of 
  

   the 
  oblique 
  border; 
  coronal 
  belt 
  sharply 
  inbeveled 
  to 
  the 
  deep, 
  

   slightly 
  produced 
  basal 
  portion. 
  Coronal 
  region 
  usually 
  a 
  little 
  

   narrower 
  than 
  the 
  base, 
  which 
  extends 
  slightly 
  beyond 
  the 
  limits 
  of 
  

   the 
  enamel 
  fold 
  in 
  the 
  lateral 
  borders, 
  the 
  worn 
  outer 
  surface 
  pre- 
  

   senting 
  a 
  pimple 
  lateral 
  convexity, 
  but 
  in 
  the 
  middle 
  and 
  toward 
  

   the 
  inner 
  margin 
  showing 
  more 
  or 
  less 
  distinct, 
  subangular 
  sulci 
  

  

  ■M 
  

  

  