﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  63 
  

  

  This 
  genus 
  presents 
  the 
  same 
  peculiarity 
  of 
  dentition 
  as 
  the 
  Plerodon 
  Meyer 
  {JDiplocy- 
  

   nodus 
  Pomel) 
  of 
  the 
  European 
  Miocenes. 
  The 
  P. 
  plenidens, 
  and 
  P. 
  ratelii 
  are 
  both 
  of 
  

   the 
  Crocodilian 
  type 
  of 
  cranium, 
  the 
  rami 
  of 
  the 
  mandible 
  with 
  curved 
  extremity 
  and 
  

   short 
  symphysis, 
  while 
  Thecachampsa 
  is 
  a 
  gavial, 
  Avith 
  very 
  long 
  symphysis 
  and 
  slender 
  

   muzzle. 
  I 
  have 
  seen 
  but 
  one 
  cervical 
  vertebra 
  from 
  American 
  tertiaries, 
  and 
  that 
  is 
  of 
  the 
  

   type 
  of 
  Thoracosaurus 
  ; 
  hence 
  this 
  character 
  cannot 
  be 
  certainly 
  ascribed 
  to 
  Thecachampsa. 
  

  

  Three 
  species 
  appear 
  to 
  exist 
  in 
  our 
  Miocene 
  beds. 
  The 
  T. 
  sicaria 
  indicates 
  in 
  its 
  

   slender 
  mandible 
  one 
  character 
  of 
  the 
  genus 
  ; 
  it 
  shows 
  the 
  surface 
  to 
  have 
  been 
  ridged 
  

   and 
  pitted 
  as 
  in 
  other 
  Crocodilia. 
  The 
  T. 
  antiqua 
  Leidy 
  indicates 
  in 
  its 
  dorsal 
  vertebra, 
  

   a 
  smaller 
  hypapophysis 
  than 
  in 
  the 
  known 
  species 
  of 
  Crocodilus. 
  T. 
  sericodon 
  Cope 
  is 
  

   only 
  known 
  from 
  its 
  teeth. 
  The 
  teeth 
  of 
  the 
  three 
  species 
  may 
  be 
  thus 
  distinguished. 
  It 
  

   must 
  be 
  mentioned 
  that 
  I 
  have 
  but 
  one 
  tooth 
  of 
  T. 
  sicaria, 
  three 
  of 
  T. 
  antiqua 
  and 
  six 
  of 
  

   T. 
  sericodon. 
  In 
  the 
  first 
  the 
  tooth 
  has 
  a 
  lenticular 
  section 
  a 
  short 
  distance 
  below 
  the 
  tip, 
  

   owing 
  to 
  the 
  great 
  development 
  of 
  the 
  lateral 
  cutting 
  ridges, 
  and 
  the 
  compression 
  of 
  the 
  

   crown 
  at 
  their 
  bases. 
  In 
  the 
  other 
  two, 
  these 
  ridges 
  are 
  much 
  less 
  developed; 
  in 
  T. 
  

   antiquus 
  they 
  exist 
  only 
  towards 
  the 
  tip 
  on 
  the 
  inner 
  or 
  concave 
  face 
  of 
  the 
  tooth, 
  while 
  

   in 
  T. 
  sericodon 
  they 
  extend 
  more 
  than 
  half 
  the 
  length 
  of 
  the 
  crown 
  towards 
  the 
  base, 
  on 
  

   the 
  inner 
  side. 
  

  

  THECACHAMPSA 
  SICARIA, 
  Cope. 
  

  

  Proceed. 
  Ac. 
  Nat. 
  Sci., 
  Phila., 
  1869, 
  8. 
  

  

  This 
  species 
  is 
  represented 
  by 
  a 
  lumbar 
  vertebra, 
  an 
  imperfect 
  crown 
  of 
  a 
  tooth, 
  and 
  a 
  portion 
  of 
  the 
  under 
  jaw. 
  

   They 
  were 
  submitted 
  to 
  me 
  by 
  Philip 
  T. 
  Tyson, 
  State 
  Geologist 
  of 
  Maryland, 
  who 
  procured 
  them 
  from 
  near 
  the 
  

   mouth 
  of 
  the 
  Patuxent 
  River, 
  along 
  with 
  the 
  remains 
  of 
  Eschrichtius, 
  Physeter, 
  and 
  other 
  Cetacea. 
  

  

  Tire 
  portion 
  of 
  mandible 
  indicates 
  an 
  animal 
  of 
  a 
  size 
  considerably 
  exceeding 
  both 
  the 
  Gavial 
  of 
  India 
  and 
  the 
  

   Thoracasaurus 
  of 
  the 
  Cretaceous 
  of 
  this 
  country. 
  It 
  contains 
  all 
  or 
  parts 
  of 
  alveolae 
  of 
  six 
  teeth. 
  Opposite 
  the 
  

   fourth 
  alveolus 
  from 
  the 
  front, 
  the 
  margin 
  diverges 
  slightly 
  from 
  the 
  median 
  line, 
  indicating 
  the 
  position 
  of 
  the 
  

   distal 
  extremity 
  of 
  the 
  splenial 
  bone. 
  The 
  slight 
  degree 
  of 
  this 
  obliquity 
  indicates 
  an 
  extensive 
  contact 
  of 
  these 
  

   elements, 
  and 
  not 
  a 
  symphysis 
  formed 
  merely 
  by 
  union 
  of 
  the 
  dentary 
  elements 
  as 
  in 
  Mecistops 
  and 
  Crocodilus. 
  As 
  

   no 
  curvature 
  appears 
  at 
  the 
  anterior 
  extremity 
  of 
  the 
  fragment, 
  and 
  the 
  alveolae 
  are 
  similar 
  to 
  those 
  succeeding, 
  it 
  

   has 
  evidently 
  not 
  been 
  broken 
  from 
  the 
  anterior 
  portion 
  of 
  the 
  symphysis. 
  The 
  nutritious 
  canal 
  of 
  the 
  ramus 
  is 
  thus 
  

   nowhere 
  exposed, 
  but 
  is 
  enclosed 
  in 
  the 
  long 
  symphysis. 
  

  

  The 
  upper 
  face 
  of 
  the 
  ramus 
  is 
  convex, 
  most 
  so 
  anteriorly. 
  Its 
  lateral 
  and 
  inferior 
  face 
  is 
  more 
  convex 
  than 
  in 
  

   other 
  Gavials 
  which 
  I 
  have 
  noticed, 
  especially 
  posteriorly. 
  Its 
  surface 
  is 
  coarsely 
  sulcate, 
  and 
  with 
  numerous 
  small 
  

   foramina. 
  A 
  larger 
  space 
  than 
  elsewhere 
  is 
  seen 
  between 
  the 
  two 
  median 
  alveolae, 
  which 
  is 
  occupied 
  by 
  a 
  deep 
  con- 
  

   cavity 
  for 
  the 
  reception 
  of 
  a 
  large 
  tooth 
  of 
  the 
  maxillary 
  series. 
  This 
  indicates 
  an 
  irregularity 
  in 
  the 
  size 
  of 
  the 
  

   teeth 
  of 
  that 
  series, 
  as 
  in 
  the 
  Crocodiles, 
  and 
  not 
  an 
  equality 
  as 
  in 
  other 
  Gavials. 
  On 
  placing 
  the 
  fragment 
  in 
  position 
  

   the 
  teeth 
  are 
  seen 
  to 
  have 
  diverged 
  at 
  an 
  angle 
  of 
  45°. 
  

  

  The 
  specimen 
  had 
  laid 
  sufficiently 
  long 
  in 
  the 
  Miocene 
  ocean 
  bottom 
  to 
  have 
  been 
  fixed 
  upon 
  by 
  barnacles 
  and 
  

   oysters, 
  as 
  a 
  place 
  of 
  abode. 
  That 
  it 
  had 
  not 
  remained 
  unburied 
  very 
  long 
  is 
  evident 
  from 
  the 
  small 
  size 
  which 
  these 
  

   parasites 
  had 
  attained 
  ; 
  and 
  that 
  it 
  was 
  buried 
  in 
  Miocene 
  deposits 
  and 
  not 
  worn 
  by 
  a 
  more 
  modern 
  sea, 
  is 
  testified 
  

   to 
  by 
  the 
  Miocene 
  shells 
  (Turritella, 
  etc.), 
  whose 
  fragments 
  were 
  removed 
  from 
  its 
  cavities 
  with 
  the 
  sandy 
  clay 
  of 
  its 
  

   place 
  of 
  burial. 
  The 
  teeth 
  have 
  been 
  broken 
  off 
  in 
  this 
  rough 
  contact 
  with 
  the 
  elements, 
  but 
  I 
  procured 
  a 
  large 
  and 
  

   characteristic 
  portion 
  of 
  the 
  crown 
  of 
  a 
  successional 
  tooth 
  whose 
  apex 
  had 
  attained 
  to 
  the 
  level 
  of 
  the 
  edge 
  of 
  the 
  

  

  