﻿OF 
  FIVE 
  GENERA 
  OF 
  MESOZOIC 
  EEPTILES. 
  5/ 
  

  

  structure 
  of 
  the 
  pelvis 
  of 
  Metriorhynchus 
  * 
  is 
  very 
  peculiar, 
  aud 
  with 
  

   the 
  aid 
  of 
  the 
  above-mentioned 
  skeleton 
  the 
  three 
  elements 
  of 
  this 
  

   girdle 
  can 
  readily 
  be 
  detected, 
  in 
  a 
  somewhat 
  imperfect 
  condition, 
  

   in 
  the 
  slab 
  containing 
  the 
  hinder 
  portion 
  of 
  the 
  type 
  of 
  Geosaurus, 
  

   these 
  bones 
  corresponding 
  in 
  all 
  respects 
  with 
  those 
  of 
  Metrio- 
  

   rhynchus. 
  

  

  There 
  appears, 
  moreover, 
  to 
  be 
  no 
  doubt 
  that 
  some 
  of 
  the 
  skulls 
  

   described 
  by 
  Wagner 
  under 
  the 
  name 
  of 
  Cricosaurus, 
  which 
  were 
  

   obtained 
  from 
  the 
  same 
  Lower 
  Kimeridgian 
  horizon 
  as 
  Geosaurus, 
  

   are 
  identical 
  with 
  that 
  genus 
  ; 
  although 
  one 
  of 
  them, 
  I 
  believe, 
  

   belongs 
  to 
  Metriorhynchus. 
  These 
  specimens, 
  together 
  with 
  a 
  skull 
  

   in 
  the 
  Natural 
  History 
  Museum, 
  show 
  that 
  there 
  was 
  no 
  lateral 
  

   vacuity 
  in 
  the 
  mandible 
  of 
  Geosaurus, 
  and 
  that 
  the 
  upper 
  surface 
  

   of 
  the 
  skull 
  was 
  almost 
  or 
  quite 
  devoid 
  of 
  sculpture. 
  The 
  teeth, 
  as 
  

   shown 
  by 
  several 
  specimens, 
  have 
  laterally 
  compressed 
  crowns 
  

   bearing 
  a 
  pair 
  of 
  well-defined 
  carinas, 
  which 
  are 
  marked 
  by 
  fine 
  

   serrations, 
  their 
  lateral 
  surfaces 
  being 
  smooth 
  and 
  polished. 
  

  

  In 
  Metriorhynchus, 
  on 
  the 
  other 
  hand, 
  as 
  I 
  gather 
  from 
  Mr. 
  Leeds's 
  

   examples 
  and 
  those 
  figured 
  by 
  E. 
  Deslongchamps, 
  the 
  upper 
  surface 
  

   of 
  the 
  skull 
  is 
  more 
  or 
  less 
  distinctly 
  sculptured 
  ; 
  the 
  mandible, 
  at 
  

   least 
  frequently, 
  has 
  a 
  lateral 
  vacuity 
  : 
  while 
  the 
  teeth 
  have 
  sub- 
  

   cylindrical 
  crowns, 
  without 
  distinct 
  carinas, 
  and 
  with 
  the 
  enamel 
  

   marked 
  by 
  longitudinal 
  rugosities. 
  

  

  These 
  differences 
  would 
  appear 
  to 
  indicate 
  the 
  right 
  of 
  Geosaurus 
  

   and 
  Metriorhynchus 
  to 
  stand 
  as 
  distinct, 
  although 
  closely 
  allied, 
  

   genera. 
  If, 
  however, 
  the 
  genus 
  Dacosaurusf, 
  which 
  is 
  likewise 
  of 
  

   Kimeridgian 
  and 
  Oxfordian 
  age, 
  be 
  compared 
  with 
  Geosaurus, 
  it 
  

   appears 
  that 
  no 
  characters 
  can 
  be 
  detected 
  by 
  which 
  the 
  two 
  are 
  

   distinguishable. 
  Thus 
  the 
  skull 
  has 
  the 
  same 
  absence 
  of 
  sculp- 
  

   ture 
  ; 
  the 
  mandible, 
  as 
  Mr. 
  Hulke 
  has 
  shown, 
  has 
  no 
  lateral 
  

   vacuity; 
  and 
  the 
  structure 
  of 
  the 
  teeth 
  is 
  identical. 
  "We 
  have, 
  

   indeed, 
  no 
  evidence 
  as 
  to 
  the 
  presence 
  of 
  sclerotic 
  plates, 
  but 
  

   the 
  absence 
  of 
  scutes 
  is 
  very 
  noticeable 
  in 
  the 
  imperfect 
  skeleton 
  

   described 
  by 
  Mr. 
  Hulke. 
  In 
  the 
  absence, 
  therefore, 
  of 
  any 
  ap- 
  

   parent 
  distinction, 
  I 
  think 
  the 
  genus 
  Dacosaurus 
  must 
  be 
  merged 
  

   in 
  the 
  earlier 
  Geosaurus, 
  in 
  which 
  the 
  type 
  species 
  was 
  originally 
  

   placed 
  by 
  Plieninger. 
  

  

  The 
  Metriorhyn 
  chinas, 
  or 
  Geosaurinas, 
  will 
  therefore 
  be 
  a 
  sub- 
  

   family 
  of 
  the 
  Teleosauridas, 
  containing 
  the 
  genera 
  Geosaurus 
  and 
  

   Metriorhynchus, 
  and 
  typically 
  characterized, 
  in 
  addition 
  to 
  the 
  fea- 
  

   tures 
  pointed 
  out 
  in 
  the 
  diagnosis 
  given 
  in 
  the 
  ' 
  Catalogue 
  ' 
  above 
  

   cited 
  i, 
  by 
  the 
  absence 
  of 
  dermal 
  scutes 
  and 
  the 
  presence 
  of 
  sclerotic 
  

   plates. 
  Crocodilcemus 
  of 
  Jourdan 
  § 
  has 
  a 
  well-developed 
  armour, 
  

   and 
  is 
  therefore 
  entitled 
  to 
  distinction 
  from 
  Metriorhynchus 
  ; 
  but 
  

  

  * 
  An 
  interesting 
  paper 
  on 
  the 
  skeleton 
  of 
  Metriorhynchus 
  has 
  been 
  recently 
  

   read 
  by 
  Mr. 
  Hulke 
  before 
  the 
  Zoological 
  Society. 
  

  

  t 
  Including 
  Steneosaurus 
  Manseli, 
  Hulke, 
  = 
  Plesiosuchus, 
  Owen. 
  See 
  the 
  

   writer's 
  ' 
  Catalogue 
  of 
  Fossil 
  Eeptilia 
  and 
  Amphibia 
  in 
  the 
  British 
  Museum/ 
  

   pt. 
  i. 
  p. 
  92 
  (1888). 
  

  

  t 
  Page 
  91. 
  § 
  Ibid. 
  p. 
  98. 
  

  

  