﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  

  

  175 
  

  

  Arcbaeopteryx. 
  Rhamphorhynchus, 
  which 
  most 
  resembles 
  it, 
  differs 
  in 
  its 
  simple 
  teeth; 
  and 
  Dimorphodon, 
  in 
  its 
  

   opistho- 
  or 
  amphicoelian 
  vertebrae. 
  

  

  Dimorphodon 
  Owen 
  has 
  been 
  up 
  to 
  the 
  present 
  time 
  the 
  oldest 
  type 
  of 
  the 
  Pterosauria, 
  D. 
  macronyx 
  Buck, 
  occur- 
  

   ring 
  in 
  the 
  Lower 
  Lias 
  of 
  England. 
  The 
  present 
  species 
  will 
  therefore 
  be 
  of 
  much 
  interest, 
  as 
  originating 
  in 
  a 
  sup- 
  

   posed 
  Triassic 
  formation, 
  but 
  indicating 
  with 
  the 
  Megadactylus 
  more 
  probably 
  Jurassic 
  age. 
  Perhaps 
  the 
  strata 
  con- 
  

   tinuous 
  between 
  its 
  horizon 
  and 
  that 
  of 
  Belodon* 
  (Be. 
  carolinensis) 
  will 
  point 
  to 
  the 
  correctness 
  of 
  Wheatley'st 
  pro- 
  

   position, 
  that 
  " 
  The 
  true 
  position 
  may 
  be 
  determined 
  like 
  the 
  San 
  Casciano 
  beds, 
  intermediate 
  between 
  the 
  Liassic 
  

   and 
  Triassic 
  formations, 
  and 
  forming 
  a 
  separate 
  group, 
  containing 
  like 
  those 
  beds 
  its 
  own 
  peculiar 
  fossils." 
  

  

  As 
  the 
  first 
  Pterosaur 
  found 
  in 
  the 
  Mesozoic 
  formations 
  of 
  North 
  America, 
  the 
  species 
  is 
  of 
  interest 
  as 
  indicating 
  

   the 
  future 
  discovery 
  of 
  other 
  forrirs 
  of 
  the 
  same 
  sub-class, 
  which 
  wide 
  distribution 
  will 
  furnish 
  additional 
  illustra- 
  

   tions 
  or 
  the 
  persistency 
  of 
  evanescence 
  of 
  types. 
  Some 
  of 
  the 
  remains, 
  however, 
  probably 
  belong 
  to 
  the 
  Symphypoda. 
  

  

  Fig. 
  40. 
  

  

  

  m 
  

  

  V 
  

  

  PYTIIONOMORPHA. 
  

  

  Cope 
  Proceed., 
  Boston 
  Soc. 
  Nat. 
  Hist., 
  1869, 
  p. 
  253. 
  

  

  The 
  genus 
  Mosasaurus, 
  since 
  the 
  discovery 
  of 
  the 
  large 
  specimen 
  in 
  the 
  St. 
  Peter's 
  

   Mount, 
  at 
  Maestricht, 
  has 
  been 
  a 
  subject 
  of 
  discussion 
  by 
  many 
  palaeontologists, 
  and 
  ever 
  

  

  *Vid. 
  Cope, 
  Proceedings 
  Academy, 
  18(i6. 
  

  

  t 
  In 
  Silllman's 
  Journal 
  of 
  Science 
  and 
  Arts, 
  xxxn, 
  1861. 
  

  

  