﻿VERTEBRATES. 
  141 
  

  

  Genus 
  DELTODUS, 
  Agassiz. 
  

  

  Deltodus. 
  Agassiz, 
  MSS., 
  1859. 
  Pcecilidus 
  sublaevis; 
  Messrs. 
  J. 
  Morris 
  and 
  G. 
  E. 
  Roberts 
  

   1862, 
  Quarterly 
  Jour. 
  Geol. 
  Soe. 
  London, 
  XVIII, 
  p. 
  94; 
  Messrs. 
  Newbehby 
  and 
  Worthen' 
  

   18W), 
  Illinois 
  Geological 
  Survey. 
  II, 
  p. 
  9C; 
  Lord 
  Enniskillex, 
  1869, 
  Catalogue 
  of 
  Type 
  

   Specimens, 
  Geol. 
  Mag., 
  London, 
  VI, 
  extract, 
  p. 
  4; 
  Dr. 
  L. 
  de 
  Koninck, 
  1878, 
  Fauwe 
  du 
  

   Calcaire 
  Carbomfire 
  de 
  la 
  Belgique, 
  II, 
  p. 
  03; 
  Dr. 
  P. 
  Bigsby. 
  1878, 
  Thesaurus 
  Devonico- 
  

   Oarbomferous, 
  1878. 
  

  

  t* 
  £■&/ 
  Thsee- 
  forms' 
  have 
  thus 
  far 
  been 
  recognized 
  as 
  having 
  probably 
  

   pertained 
  to 
  one 
  and 
  the 
  same 
  generic 
  category, 
  as 
  follows 
  : 
  

  

  Mandibular 
  posterior 
  teeth 
  sub 
  -triangular 
  or 
  sub-spatulate 
  in 
  out- 
  

   line, 
  arched 
  and 
  slightly 
  spirally 
  inrolled 
  from 
  within 
  outward. 
  An- 
  

   terolateral 
  border 
  with 
  a 
  slight 
  concavity 
  in 
  its 
  course 
  from 
  the 
  inner 
  

   angle 
  to 
  the 
  inrolled 
  outer 
  margin, 
  basal 
  portion 
  channeled 
  and 
  ter- 
  

   minated 
  below 
  in 
  a 
  thin 
  rim, 
  bordered 
  above 
  by 
  the 
  inbeveled 
  belt 
  

   which 
  is 
  enveloped 
  in 
  the 
  coronal 
  enamel, 
  and 
  partaking 
  of 
  its 
  punc- 
  

   tate 
  structure 
  ; 
  postero-lateral 
  border 
  obliquely 
  converging 
  from 
  the 
  

   sub-acute 
  posterior 
  angle 
  toward 
  the 
  outer 
  margin, 
  gently 
  arched, 
  

   nearly 
  vertical, 
  basal 
  portion 
  channeled 
  and 
  defined 
  above 
  by 
  a 
  nar- 
  

   rower, 
  more 
  or 
  less 
  abruptly-rounded 
  belt 
  of 
  coronal 
  enamel; 
  inner- 
  

   margin 
  sigmoidally 
  curved, 
  broadly 
  arched 
  from 
  the 
  obtuse 
  anterior 
  

   angle 
  round 
  the 
  base 
  of 
  the 
  coronal 
  prominence, 
  with 
  a 
  concave 
  

   course 
  thence 
  to 
  the 
  sub-acute 
  posterior 
  angle. 
  Coronal 
  region 
  pre- 
  

   senting 
  a 
  prominent 
  anterior 
  ridge 
  culminating 
  in 
  a 
  more 
  or 
  less 
  

   rounded 
  crest 
  near 
  the 
  median 
  line, 
  with 
  gentle 
  inclination 
  to 
  the 
  

   antero-lateral 
  border, 
  abruptly 
  sloped 
  into 
  the 
  posterior 
  depression, 
  

   which 
  is 
  defined 
  by 
  the 
  more 
  or 
  less 
  upraised 
  border 
  forming 
  the 
  

   posterior 
  alate 
  lobe. 
  

  

  Mandibular 
  median 
  teeth 
  cuneate 
  or 
  elongate 
  sub-trapezoidal 
  in 
  

   outline, 
  relatively 
  narrow, 
  transverse 
  diameter, 
  longitudinally 
  arched 
  

   and 
  inrolled 
  at 
  the 
  outer 
  margin. 
  Postero-lateral 
  border 
  with 
  a 
  

   slight 
  sigmoidal 
  curvature 
  and 
  somewhat 
  oblique 
  outward 
  and 
  for- 
  

   ward 
  course, 
  basal 
  portion 
  channeled 
  and 
  terminating 
  in 
  a 
  narrow 
  

   edge, 
  coronal 
  belt 
  relatively 
  wide, 
  abruptly 
  beveled 
  to 
  the 
  narrow 
  

   ridge 
  limiting 
  the 
  basal 
  furrow, 
  the 
  articular 
  border 
  nicely 
  co-adapted 
  

   to 
  that 
  of 
  the 
  conterminous 
  posterior 
  tooth 
  ; 
  antero-lateral 
  border 
  rel- 
  

   atively 
  short, 
  less 
  oblique 
  in 
  its 
  outward 
  and 
  forward 
  course, 
  basal 
  por- 
  

   tion 
  relatively 
  narrow, 
  channeled, 
  limited 
  above 
  by 
  the 
  rounded, 
  inbev- 
  

   eled 
  enamel 
  fold 
  ; 
  the 
  inner 
  margin 
  is 
  peculiar 
  for 
  the 
  obliquity 
  of 
  the 
  

   anterior 
  half 
  and 
  sudden 
  deflection 
  nearly 
  at 
  right-angles 
  in 
  round- 
  

   ing 
  the 
  base 
  of 
  the 
  coronal 
  ridge, 
  with 
  a 
  slight 
  concavity 
  in 
  its 
  

   course 
  thence 
  to 
  the 
  sub-acute 
  posterior 
  angle 
  ; 
  coronal 
  region 
  tra- 
  

   versed 
  by 
  a 
  strong 
  median 
  ridge, 
  culminating 
  in 
  a 
  rounded 
  crest, 
  

  

  .-■■j- 
  

  

  