﻿402 
  PROCEEDrNTGS 
  OF 
  THE 
  NATIONAL 
  IVIUSEUM 
  vol. 
  los 
  

  

  Suborder 
  SERPENTES 
  

   Family 
  Boidae 
  

  

  Calamagras 
  sp. 
  

  

  USNM 
  19082, 
  a 
  single 
  thoracic 
  vertebra 
  from 
  the 
  Lower 
  Oligocene 
  

   of 
  locality 
  No. 
  24BW18, 
  appears 
  to 
  be 
  referable 
  to 
  this 
  genus. 
  As 
  

   pointed 
  out 
  by 
  Gilmore 
  (1938, 
  p. 
  36), 
  this 
  genus 
  is 
  difficult 
  to 
  distin- 
  

   guish 
  from 
  the 
  following 
  one, 
  but 
  in 
  view 
  of 
  the 
  very 
  limited 
  state 
  of 
  

   our 
  knowledge 
  it 
  will 
  be 
  convenient 
  to 
  retain 
  one 
  genus 
  for 
  the 
  small 
  

   boids 
  of 
  the 
  Oligocene 
  and 
  the 
  other 
  for 
  the 
  Miocene. 
  

  

  Ogmophis 
  arenarum 
  Douglass 
  

  

  USNM 
  19083, 
  two 
  thoracic 
  vertebrae 
  and 
  the 
  neural 
  arch 
  of 
  a 
  third 
  

   in 
  a 
  connected 
  series, 
  from 
  the 
  Lower 
  Miocene 
  of 
  Canyon 
  Ferry, 
  are 
  

   referred 
  to 
  this 
  species 
  on 
  the 
  basis 
  of 
  the 
  ovate 
  central 
  articulations, 
  

   but 
  the 
  material 
  is 
  too 
  limited 
  to 
  contribute 
  anything 
  to 
  our 
  knowledge 
  

   of 
  the 
  genus. 
  

  

  It 
  is 
  interesting 
  to 
  note 
  here 
  that 
  of 
  the 
  two 
  other 
  reptilian 
  types 
  

   commonly 
  found 
  in 
  the 
  Oligocene 
  of 
  the 
  plains, 
  one, 
  the 
  crocodilians, 
  

   is 
  unknown 
  and 
  the 
  other, 
  the 
  turtles, 
  is 
  represented 
  only 
  by 
  the 
  

   terrestrial 
  types. 
  No 
  fragments 
  indicative 
  of 
  any 
  of 
  the 
  aquatic 
  

   types 
  have 
  yet 
  been 
  found. 
  On 
  the 
  other 
  hand, 
  the 
  aquatic 
  types 
  

   of 
  tm-tles 
  are 
  rare 
  in 
  the 
  White 
  River 
  deposits. 
  

  

  Class 
  MAMMALIA 
  

  

  Order 
  MARSUPIALIA 
  

  

  Suborder 
  POLYPROTODONTIA 
  

  

  Family 
  Didelphidae 
  

  

  Peratherium 
  fugax 
  Cope 
  

  

  USNM 
  18953, 
  left 
  mandible 
  with 
  P2-M4; 
  USNM 
  18954, 
  left 
  man- 
  

   dible 
  with 
  P1-M4. 
  Both 
  specimens 
  are 
  from 
  locality 
  No. 
  24LC15. 
  

  

  These 
  specimens 
  are 
  nearly 
  twice 
  the 
  size 
  of 
  P. 
  titanelix 
  Matthew 
  

   from 
  Pipestone 
  Springs 
  and 
  only 
  slightly 
  larger 
  than 
  the 
  measure- 
  

   ments 
  Scott 
  (1941, 
  p. 
  962) 
  gives 
  for 
  this 
  species. 
  An 
  examination 
  of 
  

   the 
  material 
  in 
  the 
  U. 
  S. 
  National 
  Museum 
  referable 
  to 
  this 
  genus 
  

   shows 
  that 
  the 
  variation 
  in 
  the 
  characters 
  of 
  the 
  teeth 
  and 
  jaws 
  is 
  

   greater 
  in 
  this 
  genus 
  than 
  in 
  the 
  higher 
  mammals. 
  It 
  is 
  probable, 
  as 
  

   Scott 
  points 
  out, 
  that 
  there 
  are 
  only 
  two 
  valid 
  species, 
  a 
  large 
  and 
  a 
  

   small, 
  in 
  the 
  Middle 
  Oligocene 
  of 
  North 
  America. 
  Measurements 
  

   of 
  teeth 
  (in 
  millimeters): 
  

  

  USNM1895S 
  USNM 
  18954 
  

  

  Pi-j 
  6.0 
  6.3 
  

  

  Mi-4 
  7.5 
  7.1 
  

  

  