﻿VEETEBEATES. 
  239 
  

  

  Ctenacanthus 
  .cannalieatus, 
  St. 
  J. 
  and 
  W. 
  

  

  PI. 
  XXI, 
  Pig. 
  3. 
  

  

  Fin-spine 
  long 
  and 
  slender, 
  very 
  gradually 
  tapering, 
  moderately 
  

   arched 
  along 
  the 
  dorsal 
  edge, 
  much 
  compressed 
  laterally, 
  posteriorly 
  

   truncated, 
  wedge-shaped 
  in 
  transverse 
  section, 
  pulp 
  cavity 
  small, 
  

   elongate 
  oval 
  in 
  outline 
  and 
  confined 
  within 
  the 
  posterior 
  half 
  of 
  

   the 
  diameter 
  of 
  the 
  spine. 
  Posterior 
  face 
  slightly 
  depressed 
  and 
  

   traversed 
  hy 
  a 
  faint 
  median 
  keel, 
  postero-lateral 
  angles 
  sharp, 
  

   the 
  slightly 
  raised 
  inner 
  border 
  showing 
  indications 
  of 
  moderately 
  

   spaced, 
  minute, 
  laterally 
  compressed 
  denticles. 
  Lateral 
  surfaces 
  

   gently 
  convex 
  transversely 
  and 
  regularly 
  converging 
  toward 
  the 
  

   sharply 
  rounded 
  anterior 
  edge, 
  and 
  occupied 
  by 
  more 
  or 
  less 
  regu- 
  

   larly 
  rounded 
  costse, 
  intercostal 
  furrows 
  deep, 
  about 
  half 
  the 
  breadth 
  

   of 
  the 
  ridges. 
  The 
  posterior 
  cost* 
  are 
  enveloped 
  in 
  a 
  smooth 
  

   enamel 
  coating 
  ; 
  toward 
  the 
  front 
  they 
  show 
  delicate 
  flexuous 
  sharp- 
  

   crested 
  longitudinal 
  lines, 
  and 
  the 
  second 
  or 
  third 
  rib 
  from 
  the 
  

   dorsal 
  ridge 
  becomes 
  distinctly 
  interrupted 
  by 
  transverse 
  carinas, 
  at 
  

   the 
  same 
  time 
  retaining 
  the 
  thread-like 
  lines 
  ; 
  the 
  remaining 
  ridges 
  

   are 
  more 
  and 
  more 
  strongly 
  marked 
  by 
  the 
  transverse 
  carinae, 
  the 
  

   anterior 
  one 
  strongest 
  of 
  all. 
  The 
  carinas 
  cross 
  the 
  ribs 
  obliquely, 
  

   culminating 
  above 
  in 
  delicate 
  sharp 
  crests, 
  most 
  prominent 
  along 
  

   the 
  anterior 
  margin 
  where 
  they 
  are 
  ornamented 
  by 
  a 
  few 
  sharp 
  

   radiating 
  lines 
  producing 
  a 
  pectinated 
  or 
  notched 
  appearance 
  in 
  

   that 
  side 
  ; 
  the 
  anterior 
  ridge 
  is 
  prominent, 
  somewhat 
  compressed 
  

   laterally, 
  and 
  marked 
  by 
  similar 
  slightly 
  asymmetrical 
  transverse 
  

   ridges, 
  which, 
  however, 
  are 
  equally 
  developed 
  in 
  either 
  margin, 
  pro- 
  

   ducing 
  a 
  faint 
  undulation 
  along 
  the 
  rounded 
  crest. 
  

  

  The 
  collection 
  of 
  Dr. 
  Hambach 
  affords 
  a 
  small 
  section 
  of 
  one 
  of 
  

   the 
  long, 
  slender 
  spines 
  of 
  Ctenacanthus 
  different 
  from 
  any 
  form 
  

   heretofore 
  derived 
  from 
  the 
  Chester 
  formation. 
  The 
  spine 
  is 
  inti- 
  

   mately 
  related 
  to 
  Ct. 
  gracillimus, 
  N. 
  and 
  W., 
  of 
  the 
  St. 
  Louis 
  lime- 
  

   stone, 
  for 
  which 
  indeed 
  it 
  might 
  be 
  mistaken 
  on 
  casual 
  observation. 
  

  

  However, 
  searching 
  comparisons 
  with 
  the 
  latter 
  species 
  discloses 
  

   certain 
  details 
  in 
  ornamentation 
  which 
  may 
  indicate 
  for 
  the 
  Chester 
  

   form 
  a 
  specifically 
  distinct, 
  though 
  closely 
  allied, 
  character. 
  While 
  

   the 
  form 
  and 
  general 
  appearance 
  of 
  the 
  latter 
  is 
  strikingly 
  like 
  the 
  

   St. 
  Louis 
  spine, 
  there 
  is 
  a 
  marked 
  dissimilarity 
  in 
  the 
  character 
  of 
  

  

  