﻿VERTEBRATES. 
  139 
  

  

  from 
  Poscilodus 
  St. 
  Ludovici, 
  and 
  the 
  presence 
  of 
  longitudinal 
  folds 
  

   in 
  the 
  median 
  depression 
  offers 
  a 
  contrast 
  with 
  P. 
  Cestricnsis. 
  

  

  Geological 
  position 
  and 
  locality: 
  Lower 
  Carboniferous 
  limestone 
  

   strata 
  ; 
  vicinity 
  of 
  Santa 
  Fe, 
  New 
  Mexico. 
  

  

  Pcectlodus 
  carbonaeius, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  VIII, 
  Pig. 
  20-21. 
  

  

  Teeth 
  of 
  medium 
  or 
  small 
  size, 
  known 
  from 
  the 
  opposed 
  terminal 
  

   forms 
  of 
  the 
  upper 
  and 
  lower 
  jaws. 
  

  

  Posterior 
  teeth 
  of 
  the 
  mandibles 
  characterized 
  by 
  the 
  relatively 
  low 
  

   coronal 
  ridges, 
  the 
  principal 
  ridge 
  situate 
  considerably 
  posterior 
  of 
  

   a 
  line 
  traversing 
  the 
  middle 
  of 
  the 
  tooth 
  in 
  the 
  direction 
  of 
  inroll- 
  

   ment, 
  broadly 
  arched 
  transversely 
  along 
  the 
  inner 
  margin 
  but 
  form 
  - 
  

   ing 
  a 
  narrow 
  angularly 
  rounded 
  ridge 
  toward 
  the 
  outer 
  margin; 
  

   anterior 
  ridge 
  narrow, 
  sharply 
  rounded 
  along 
  the 
  crest, 
  steeply 
  

   sloping 
  to 
  the 
  articular 
  border 
  of 
  the 
  antero-lateral 
  side, 
  and 
  nearly 
  

   equally 
  abruptly 
  inclined 
  behind 
  into 
  the 
  comparatively 
  wide 
  median 
  

   depression 
  separating 
  it 
  from 
  the 
  principal 
  ridge, 
  and 
  which 
  is 
  tra- 
  

   versed 
  by 
  a 
  slight 
  longitudinal 
  fold 
  ; 
  posterior 
  depression 
  defined 
  on 
  

   the 
  one 
  side 
  by 
  the 
  steep 
  slope 
  of 
  the 
  principal 
  ridge, 
  and 
  on 
  the 
  

   other 
  moderately 
  rising 
  into 
  the 
  comparatively 
  narrow 
  alate 
  expan- 
  

   sion 
  of 
  the 
  postero-lateral 
  border, 
  which 
  terminates 
  in 
  the 
  moder- 
  

   ately 
  produced 
  posterior 
  angle 
  ; 
  postero-lateral 
  border 
  nearly 
  vertical 
  

   or 
  produced 
  slightly 
  outward 
  interiorly, 
  defined 
  along 
  the 
  upper 
  edge 
  

   by 
  the 
  narrow 
  inbeveled 
  enamel 
  fold 
  and 
  slightly 
  channeled 
  ; 
  antero- 
  

   lateral 
  border 
  not 
  well 
  shown 
  in 
  the 
  accessible 
  examples. 
  Breadth 
  

   of 
  tooth 
  across 
  the 
  inner 
  margin 
  17 
  mm. 
  ; 
  length 
  of 
  antero-latera/ 
  

   articular 
  edge 
  4.5 
  to 
  5 
  mm. 
  ; 
  longitudinal 
  diameter 
  along 
  principal 
  

   riclge 
  to 
  inrolled 
  outer 
  margin 
  about 
  13.5 
  mm. 
  

  

  Posterior 
  teeth 
  of 
  the 
  maxillaries 
  in 
  general 
  outline 
  elliptical, 
  rather 
  

   strongly 
  and 
  spirally 
  inrolled, 
  broadly 
  arched 
  outward 
  along 
  the 
  inner 
  

   margin 
  with 
  a 
  slight 
  concavity 
  in 
  the 
  region 
  of 
  the 
  median 
  coronal 
  

   depression; 
  postero-lateral 
  border 
  terminating 
  in 
  a 
  sharply 
  rounded 
  

   angle, 
  thence 
  gently 
  and 
  regularly 
  curved 
  in 
  its 
  rapid 
  convergence 
  

   toward 
  point 
  of 
  inrollment, 
  the 
  relatively 
  strong 
  enamel 
  fold 
  inbev- 
  

   eled 
  to 
  the 
  basal 
  rim 
  from 
  which 
  it 
  is 
  defined 
  by 
  a 
  deep 
  narrow 
  

   groove 
  ; 
  antero-lateral 
  border 
  very 
  oblique 
  outward 
  and 
  forward 
  to 
  

   the 
  inner 
  margin, 
  and 
  also 
  . 
  apparently 
  defined 
  along 
  the 
  upper 
  edge 
  

   by 
  a 
  narrow 
  inbeveled 
  enamel 
  fold. 
  Coronal 
  contour 
  regularly 
  and 
  

   rather 
  strongly 
  arched 
  longitudinally, 
  moderately 
  so 
  transversely; 
  

  

  