﻿412 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  103 
  

  

  distinct, 
  posterior 
  cingulum 
  not 
  uniting 
  with 
  entoconid; 
  M3 
  sub 
  trian- 
  

   gular 
  in 
  outline, 
  sharply 
  constricted 
  behind 
  protoconid, 
  lingual 
  portion 
  

   of 
  anterior 
  cingulum 
  short 
  but 
  distinct, 
  posterior 
  arm 
  of 
  protoconid 
  

   extending 
  to 
  lingual 
  border 
  of 
  tooth 
  and 
  united 
  with 
  metaconid 
  at 
  

   base, 
  no 
  mesolophid. 
  

  

  Variation. 
  — 
  In 
  one 
  specimen 
  the 
  anterior 
  arm 
  of 
  the 
  metaconid 
  is 
  

   united 
  to 
  the 
  anteroconid 
  while 
  the 
  protoconid 
  is 
  not. 
  In 
  one, 
  both 
  

   are 
  united 
  to 
  the 
  anteroconid. 
  The 
  mesolophid 
  of 
  Mi 
  and 
  M2 
  is 
  

   variable 
  in 
  length 
  but 
  is 
  always 
  distinct. 
  In 
  two 
  specimens 
  the 
  

   posterior 
  arm 
  of 
  the 
  protoconid 
  M2 
  and 
  M3 
  is 
  shorter 
  than 
  in 
  the 
  type, 
  

   but 
  the 
  teeth 
  agree 
  in 
  other 
  particulars. 
  

  

  The 
  short 
  mesolophid 
  on 
  M2 
  is 
  very 
  suggestive 
  of 
  Cricetodon, 
  but 
  

   the 
  evidence 
  does 
  not 
  warrant 
  referring 
  this 
  material 
  to 
  that 
  genus. 
  

   Measurements 
  of 
  teeth 
  (in 
  millimeters): 
  

  

  Ml 
  Mi 
  Afi 
  

  

  Ml-: 
  

  

  USNM 
  No. 
  Length 
  Width 
  Length 
  Width 
  Length 
  Width 
  

  

  18749 
  8.0 
  2.7 
  1.9 
  2.6 
  2.2 
  2.5 
  2.0 
  

  

  18751 
  8.2 
  2.9 
  2.2 
  2.6 
  2.4 
  2.5 
  2.2 
  

  

  18748 
  (Type) 
  7.8 
  2.5 
  1.9 
  2.8 
  2.2 
  2.5 
  2.1 
  

  

  18753 
  --- 
  2.8 
  1.8 
  2.5 
  2.2 
  2.0 
  

  

  18754 
  --- 
  -- 
  7.9 
  2.8 
  2.1 
  2.6 
  2.2 
  2.6 
  2.1 
  

  

  18750 
  7.7 
  2.6 
  1.8 
  2.3 
  2.0 
  2.6 
  2.0 
  

  

  18752 
  - 
  - 
  - 
  2.5 
  2.1 
  2.7 
  2.1 
  

  

  Eumya 
  latidena, 
  new 
  species 
  

  

  Holotype.—VSNM 
  18772 
  (fig. 
  46), 
  right 
  mandible 
  of 
  young 
  individ- 
  

   ual 
  with 
  Mi_3. 
  

  

  Horizon 
  and 
  locality. 
  — 
  Middle 
  Ohgocene, 
  Orellan; 
  SE)^SE}i 
  sec. 
  10, 
  

   T. 
  10 
  N., 
  R. 
  1 
  W., 
  of 
  the 
  Montana 
  prime 
  meridian, 
  about 
  Yt 
  mile 
  

   southeast 
  of 
  Canyon 
  Ferry, 
  Lewis 
  and 
  Clark 
  County, 
  Mont. 
  

  

  Referred 
  material— 
  USNM 
  18764-71, 
  18773-80, 
  16 
  mandibles 
  

   from 
  the 
  same 
  locality. 
  

  

  Description 
  of 
  type. 
  — 
  Mj 
  elongate, 
  anteroconid 
  small, 
  protoconid 
  

   united 
  to 
  anteroconid 
  and 
  metaconid, 
  mesolophid 
  well 
  developed 
  and 
  

   distinct, 
  posterior 
  cingulum 
  not 
  united 
  with 
  entoconid; 
  M2 
  quad- 
  

   rangular, 
  longer 
  than 
  wide, 
  anterior 
  cingulum 
  extending 
  across 
  front 
  

   of 
  the 
  tooth, 
  lingual 
  portion 
  shorter 
  than 
  the 
  labial, 
  both 
  protoconid 
  

   and 
  mesoconid 
  united 
  to 
  anterior 
  cingulum, 
  posterior 
  arm 
  of 
  proto- 
  

   conid 
  not 
  united 
  to 
  metaconid 
  and 
  not 
  extending 
  to 
  Ungual 
  border 
  

   of 
  tooth, 
  mesolophid 
  obsolete, 
  posterior 
  cingulum 
  not 
  uniting 
  with 
  

   entoconid; 
  M3 
  sharply 
  constricted 
  behind 
  protoconid, 
  Ungual 
  end 
  

   of 
  anterior 
  cingulum 
  obsolete, 
  posterior 
  arm 
  of 
  protoconid 
  approaches 
  

   but 
  does 
  not 
  unite 
  with 
  metaconid, 
  no 
  mesolophid. 
  

  

  Variation. 
  — 
  The 
  material 
  assigned 
  to 
  this 
  species 
  is 
  extremely 
  

   variable 
  in 
  many 
  of 
  the 
  dental 
  characters 
  but 
  the 
  designation 
  of 
  

  

  