206 Fre~tp Musrum or Natura History — Zoétocy, Vor. X. 
and forming obtuse angles in front and behind; audital bulle small; 
teeth small. As compared with a skull of O. eliurus from Sapucay, 
Paraguay, that of O. chaparensis is slightly larger and more angular; 
the interorbital region is a little wider, higher, and more sharply edged; 
nasals broader; palatine foramina shorter. 
Measurements. Type: Total length 215; head and body 104; tail 
111; hind foot 26; ear from notch (dry) 14. Skull of type: Greatest 
length 26.8; basilar length 21; zygomatic breadth 13.5; breadth of brain- 
case 11.2; interorbital constriction 4; nasals 10.5x3.5; palatine foramina 
4.4X1.9; diastema 6.9; length of zygomatic plate 2.7; upper toothrow 3.6. 
Remarks. Although the state of knowledge of the genus Oryzomys 
makes it difficult or practically impossible to determine the exact 
relationship of isolated species, it is apparent that this one does not show 
many similarities to any of the recently described Peruvian and Bolivian 
species and it is therefore probable that its allies are among the species 
described by early authors from eastern South America. Of those 
available for comparison, O. eliurus is nearest in size but its coloration 
is of the usual type and its skull differs in various ways. The coloration 
of the under parts in O. chaparensis is characteristic, for although the 
differentiation of self-colored light areas on the pectoral and inguinal 
regions is not unusual among rodents, it is relatively rare in the genus 
Oryzomys. 
Only two specimens have been examined, an adult male and a female. 
This female was nursing young and has the mammez functionally 
enlarged and conspicuous but shows no trace of more than three pairs 
whereas four pairs are normal in Oryzomys. The absence of the ante- 
rior pair of pectoral mammz may be accidental in this specimen or 
it may be a peculiarity of the species. 
(Ecomys mamorz Thomas. 
Ten specimens, Todos Santos, Chaparé River. 
Since their external and cranial measurements agree closely with 
those of the published description of this species, there is scarcely any 
reason to doubt that these specimens are practically typical represen- 
tatives of it and so far as recorded the only ones extant except the type 
which is preserved in alcohol and therefore not trustworthy for color 
characters. The color, especially that of the under parts, as shown by 
the present series, is somewhat variable. In the majority, particularly 
those not fully mature, the rich, tawny ochraceous lateral line which 
borders the color of the upper parts widens and extends with only slight 
dilution across the middle of the belly and forward as a light wash to 
the midpectoral region. Across the middle of the belly and breast 
Ce ee 
