﻿MAMMALS 
  OF 
  NORTHERN 
  COLOMBIA 
  — 
  HERSHKOVITZ 
  55 
  

  

  distinct 
  diversification 
  within 
  the 
  genus. 
  Their 
  relationship 
  to 
  each 
  

   other 
  and 
  to 
  the 
  remaining 
  species 
  of 
  oryzomyine 
  rodents 
  is 
  best 
  

   expressed 
  by 
  conferring 
  subgeneric 
  rank 
  upon 
  them. 
  

  

  The 
  oryzomyine 
  characters 
  common 
  to 
  the 
  two 
  forms 
  described 
  

   below 
  have 
  been 
  given, 
  and 
  the 
  dental 
  terminology 
  used 
  here 
  has 
  been 
  

   defined 
  {op. 
  cit., 
  pp. 
  12-17). 
  

  

  MiCRONECTOMYS, 
  new 
  subgenus 
  (genus 
  Oryzomys) 
  

  

  Type 
  species. 
  — 
  Nectomys 
  dimidiatus 
  Thomas, 
  Ann. 
  Mag. 
  Nat. 
  Hist., 
  

   ser. 
  7, 
  vol. 
  2, 
  p. 
  586, 
  1905 
  (type 
  locality, 
  Rio 
  Escondido, 
  7 
  miles 
  below 
  

   Rama, 
  Nicaragua) 
  ; 
  Hershkovitz, 
  Mus. 
  Zool. 
  Univ. 
  Michigan 
  Misc. 
  

   Publ. 
  No. 
  58, 
  pp. 
  21, 
  22, 
  80, 
  1944. 
  

  

  Description 
  of 
  type 
  species. 
  — 
  Externally 
  similar 
  to 
  a 
  young 
  N. 
  

   squamipes; 
  smaller 
  than 
  N. 
  alfari, 
  with 
  tail 
  less 
  than 
  combined 
  length 
  

   of 
  head 
  and 
  body 
  ; 
  gray 
  keel 
  hairs 
  well 
  developed 
  as 
  in 
  typical 
  adult 
  

   Nectomys; 
  webs 
  between 
  toes 
  of 
  hind 
  feet 
  reduced, 
  as 
  in 
  N. 
  alfari; 
  

   other 
  external 
  characters 
  as 
  originally 
  described. 
  Skull 
  more 
  lightly 
  

   built 
  than 
  in 
  Nectomys, 
  rather 
  as 
  in 
  typical 
  Oryzomys; 
  supraorbital 
  

   ridges 
  little 
  developed, 
  brain 
  case 
  broad, 
  smooth 
  and 
  rounded 
  ; 
  nasals 
  

   behind 
  not 
  markedly 
  narrowed, 
  the 
  ends 
  obtusely 
  pointed; 
  incisive 
  

   foramina 
  well 
  opened, 
  wider 
  behind 
  than 
  in 
  front, 
  the 
  posterior 
  border 
  

   extending 
  slightly 
  behind 
  anterior 
  plane 
  of 
  M^ 
  ; 
  mesopterygoid 
  fossa 
  

   broad, 
  its 
  palatal 
  width 
  greater 
  than 
  crown 
  length 
  of 
  M^; 
  median 
  

   border 
  of 
  alveolar 
  branch 
  of 
  maxilla 
  behind 
  M- 
  projecting 
  as 
  a 
  ledge 
  

   over 
  posterolateral 
  palatine 
  fossa, 
  the 
  palatomaxillary 
  suture 
  at 
  this 
  

   place 
  coursing 
  on 
  internal 
  wall 
  of 
  fossa 
  and 
  hidden 
  from 
  the 
  ventral 
  

   aspect 
  ; 
  sphenopalatine 
  vacuities 
  present 
  ; 
  mastoid 
  process 
  of 
  squamosal 
  

   long 
  and 
  delicate, 
  as 
  in 
  Oryzomys; 
  zygomatic 
  plate 
  w^ide 
  but 
  less 
  

   projecting 
  than 
  in 
  typical 
  Nectomys. 
  Molars 
  of 
  type 
  much 
  worn 
  and 
  

   details 
  of 
  enamel 
  pattern 
  diflicult 
  to 
  determine 
  but 
  clearly 
  less 
  simpli- 
  

   fied 
  than 
  in 
  Nectomys. 
  Shape 
  and 
  general 
  proportions 
  of 
  molars 
  as 
  

   in 
  N. 
  alfari; 
  first 
  upper 
  molar 
  with 
  an 
  anterior 
  median 
  fold 
  ; 
  in 
  M^"^ 
  

   first 
  internal 
  folds 
  discreet 
  (coalesced 
  with 
  first 
  primary 
  folds 
  in 
  

   Nectomys) 
  ; 
  second 
  internal 
  folds 
  probably 
  coalesced 
  with 
  second 
  j)ri- 
  

   mary 
  folds 
  in 
  unworn 
  teeth; 
  second 
  secondary 
  fold 
  possibly 
  present 
  

   in 
  M^; 
  anterior 
  median 
  fold 
  of 
  first 
  lower 
  molar 
  well 
  developed; 
  

   internal 
  folds 
  1 
  and 
  2 
  present 
  in 
  Mi, 
  possibly 
  present 
  in 
  M2-3. 
  

  

  Measurements 
  of 
  the 
  type 
  (in 
  millimeters). 
  — 
  Head 
  and 
  body, 
  125; 
  

   tail, 
  115; 
  hind 
  foot, 
  28; 
  ear, 
  13; 
  condylobasal 
  length, 
  27.2; 
  zygomatic 
  

   breadth, 
  17.0; 
  length 
  of 
  nasals, 
  11.5; 
  alveolar 
  length 
  of 
  molar 
  row, 
  

   4.3 
  ; 
  least 
  interorbital 
  width, 
  5.3 
  ; 
  width 
  of 
  zygomatic 
  plate, 
  3.5 
  ; 
  inter- 
  

   parietal, 
  2.8 
  X 
  7.5 
  ; 
  crown 
  length 
  of 
  M^ 
  1.9. 
  

  

  