﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  205 
  

  

  of 
  the 
  premaxillary 
  bone. 
  These 
  laminae 
  unite 
  just 
  behind 
  the 
  second 
  premaxillary 
  teeth, 
  and 
  form 
  a 
  single 
  prominent 
  

   keel, 
  which 
  disappears 
  between 
  the 
  first 
  premaxillaries. 
  

  

  This 
  very 
  fine 
  fragment 
  of 
  one 
  of 
  our 
  largest 
  extinct 
  reptiles, 
  was 
  enclosed 
  in 
  a 
  matrix 
  

   of 
  soft 
  yellow 
  chalk. 
  It 
  was 
  lent 
  me 
  for 
  introduction 
  into 
  the 
  present 
  synopsis 
  by 
  Prof. 
  

   Agassiz, 
  of 
  Cambridge, 
  Mass. 
  We 
  look 
  with 
  interest 
  to 
  a 
  complete 
  restoration 
  of 
  this 
  

   species, 
  as 
  its 
  matrix 
  is 
  so 
  readily 
  worked. 
  

  

  LIODON 
  M1TCHILLII, 
  Dekay. 
  

  

  Geosaurus 
  miichillii, 
  Dekay, 
  Annals 
  Lye, 
  New 
  York, 
  III, 
  140. 
  Bronn, 
  Lethaea 
  Geognostica: 
  nee 
  Mosasaurus 
  

   initcliillii, 
  Leidy, 
  Cretaceous 
  Reptiles 
  U. 
  S., 
  et 
  Cope 
  olim, 
  Boston 
  Proceedings, 
  1869, 
  =M. 
  major 
  Dekay. 
  

  

  Brepanodon 
  impar, 
  Leidy, 
  Proceed. 
  Acad. 
  Nat. 
  Sci., 
  Phila., 
  1856, 
  255. 
  Lestieodus 
  impar, 
  Leidy, 
  Geolog. 
  Surv. 
  

   N. 
  Ca., 
  224, 
  figs. 
  45-6; 
  — 
  fide 
  Leidy. 
  Mosasaurus, 
  Leidy, 
  Cretaceous 
  Reptiles, 
  65 
  — 
  Tab. 
  XI, 
  1, 
  2, 
  3, 
  4. 
  

  

  This 
  species 
  is 
  well 
  characterized 
  by 
  the 
  unequal 
  size 
  of 
  its 
  pterygoid 
  teeth, 
  and 
  by 
  the 
  near 
  equality 
  of 
  some 
  of 
  

   them 
  to 
  the 
  mandibular. 
  Leidy 
  observes 
  that 
  the 
  fang 
  of 
  the 
  first 
  tooth 
  indicates 
  that 
  it 
  was 
  smaller 
  than 
  the 
  second; 
  

   the 
  second, 
  third 
  and 
  fourth 
  are 
  nearly 
  equal, 
  and 
  large, 
  then 
  the 
  first 
  and 
  fifth 
  of 
  equal 
  and 
  smaller 
  size, 
  and 
  the 
  sixth 
  

   to 
  the 
  eighth 
  successively 
  smaller. 
  The 
  teeth 
  from 
  the 
  second 
  to 
  the 
  fourth 
  are 
  nearly 
  equal 
  in 
  size 
  to 
  the 
  mandibulars, 
  

   and 
  with 
  only 
  one 
  divisional 
  cutting 
  edge. 
  The 
  mandibulars 
  present 
  two, 
  nearly 
  opposite, 
  and 
  faint 
  traces 
  of 
  facets 
  only. 
  

  

  The 
  case 
  is 
  entirely 
  different 
  with 
  the 
  M. 
  dekayi, 
  where, 
  as 
  indicated 
  by 
  the 
  measurements, 
  the 
  pterygoids 
  are 
  

   sub-equal 
  and 
  very 
  much 
  smaller 
  than 
  the 
  mandibulars. 
  

  

  Other 
  portions 
  of 
  this 
  species 
  are 
  unknown, 
  hence 
  it 
  may 
  be 
  found 
  at 
  some 
  future 
  time 
  to 
  be 
  the 
  same 
  as 
  some 
  

   other 
  here 
  described. 
  In 
  that 
  case, 
  the 
  name 
  mitchillii 
  will 
  take 
  precedence 
  over 
  any 
  subsequently 
  given. 
  

  

  From 
  the 
  lower 
  marl 
  bed, 
  Monmouth 
  Co., 
  New 
  Jersey. 
  Prof. 
  Geo. 
  H. 
  Cook. 
  

  

  LIODOX 
  L.EVIS, 
  Owen. 
  

  

  Macrosaurus 
  lozvis, 
  Owen, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  Lond., 
  1849, 
  380 
  tab. 
  Leidy, 
  1. 
  c. 
  74, 
  75; 
  (per 
  errorem 
  

   Maerosaurus 
  validus 
  Tab. 
  V 
  hujus 
  operis.) 
  

  

  Portions 
  of 
  three 
  individuals 
  referable 
  to 
  this 
  species 
  have 
  come 
  under 
  my 
  notice, 
  viz 
  : 
  two 
  vertebrae 
  and 
  a 
  radius 
  

   from 
  Monmouth 
  Co., 
  N. 
  J., 
  found 
  by 
  Dr. 
  Samuel 
  Lockwood; 
  three 
  vertebras 
  from 
  the 
  same 
  county, 
  from 
  O. 
  R. 
  Willis, 
  

   and 
  a 
  single 
  vertebra 
  from 
  Medford, 
  Burlington 
  Co., 
  from 
  Charles 
  Braddock. 
  The 
  largest 
  individual 
  of 
  the 
  three 
  is 
  

   that 
  from 
  Dr. 
  Lockwood's 
  collection, 
  which 
  is 
  nearly 
  equal 
  to 
  the 
  largest 
  of 
  the 
  M. 
  validus, 
  but 
  consider- 
  

   ably 
  less 
  than 
  that 
  of 
  the 
  M. 
  proriger. 
  The 
  cervical 
  has 
  the 
  round 
  articular 
  faces, 
  while 
  the 
  dorsals 
  

   present 
  the 
  vertically 
  ovate 
  form 
  of 
  cup 
  and 
  ball 
  characteristic 
  of 
  the 
  spe- 
  Fig. 
  49. 
  

  

  cies. 
  They 
  present 
  also 
  the 
  fine 
  striation 
  of 
  the 
  margins 
  of 
  the 
  diapo- 
  

   physes 
  and 
  of 
  other 
  articular 
  faces. 
  The 
  radius 
  has 
  the 
  outer 
  margin 
  broken 
  

   away, 
  as 
  represented 
  in 
  the 
  accompanying 
  wood 
  cut; 
  its 
  humeral 
  articular 
  face 
  

   is 
  narrow 
  ovate; 
  the 
  carpal 
  curved 
  and 
  stout. 
  The 
  bone 
  is 
  very 
  peculiar, 
  in 
  

   the 
  presence 
  of 
  a 
  short 
  sub-cylindric 
  process 
  directed 
  inwardly 
  to 
  the 
  ulna, 
  and 
  

   apparently 
  adapted 
  to 
  it 
  by 
  a 
  concave 
  articular 
  face. 
  The 
  radius 
  of 
  Clidastes 
  

   and 
  that 
  of 
  Mosasaurus 
  figured 
  by 
  Leidy 
  (VIII, 
  f. 
  10, 
  Cretac. 
  Rept.) 
  merely 
  ap- 
  

   proach 
  or 
  touch 
  the 
  ulna 
  by 
  the 
  distal 
  angle. 
  

  

  Measurements 
  of 
  Supposed 
  Radius. 
  

   Length, 
  

  

  Distal 
  width 
  preserved 
  (straight 
  line), 
  

   Proximal 
  '•' 
  " 
  

  

  Width 
  ulnar 
  articular 
  face, 
  

   A 
  small 
  portion 
  of 
  the 
  external 
  margin 
  preserved, 
  shows 
  a 
  deep 
  incurvature 
  of 
  the 
  outline. 
  

  

  AMb-BICA. 
  PHILO. 
  800. 
  — 
  VOL 
  XIV. 
  52 
  

  

  