124 



P.D. JENKINS AND A. BARNETT 



(Rheomys); Voss (personal communication) recommended an alter- 

 native ordering of this character (1 — » — > 2) so in a third analysis, 

 characters 7 and 1 2 were ordered as above and character 1 8 by this 

 alternative. 



ABBREVIATIONS USED IN THE TEXT 



BMNH - The Natural History Museum [formerly British Museum 

 (Natural History)] 



Ml, M2, M3 respectively first, second and third upper molars 

 ml, m2, m3 respectively first, second and third lower molars 



ABBREVIATIONS USED FOR TAXA IN THE 

 PAUP ANALYSIS: 



Ale Anotomys leander Thomas, 1906a 



Ctr Chibchanomys trichotis (Thomas, 1897) 



Cor Chibchanomys undescribed species 



Ihy Ichthyomys hydrobates (Winge, 1891) 



Ipi Ichthyomys pittieri (Handley & Mondolfi, 1963) 



Itw Ichthyomys tweedii Anthony, 1921 



Nmo Neusticomys monticolus Anthony, 1921 



Nve Neusticomys venezuelae (Anthony, 1929) 



Rme Rheomys mexicanus Goodwin, 1959 



Rha Rheomys raptor Goldman, 1912 



Rtt Rheomys thomasi Dickey, 1 928 



Run Rheomys underwoodi Thomas, 1906b 



RESULTS 



Chibchanomys orcesi, sp. nov. 



Holotype. BMNH 82.816, adult male, skin and skull; collectors' 

 number 148; collected 22 August 1981 by members of the Oxford 

 Expedition to Las Cajas from Lake Luspa, Las Cajas, Provincia 

 Azuay, Ecuador, 02°50'S 79°30'W, altitude 3700m. 



PARATYPES. BMNH 82.8 15, adult male, skin and skull; collectors' 

 number 146, other details as for the holotype. BMNH 84.349, adult 

 male, skin and skull; collectors' number 78; collected 7 August 1983 

 by members of the Combined Universities Expedition to Ecuador 

 1983, from Lake Llaviucu, Zorracucho Valley, Las Cajas, Provincia 

 Azuay, Ecuador, 02°5 l'S 79°0 1 ' W, altitude 3 1 00m. 



Diagnosis 



An ichthyomyine species belonging to the genus Chibchanomys in 

 the following combination of features. Dorsal pelage dull; small 

 pinnae concealed in pelage of head; tail longer than head and body; 

 manus with five separate plantar pads; hindfoot broad with well 

 developed fringing hairs; supraorbital foramina open laterally within 

 orbits; carotid circulation pattern 1. 



Differing from Chibchanomys trichotis in the following charac- 

 ters. Rhinarium light brown; philtrum present; nasals medium in 

 length, barely projecting anterior to premaxillae; orbicular apophy- 

 sis of maleus present; upper incisors slightly inclined medially; M3 

 and m3 reduced in size; anteromedian flexid absent or barely 

 indicated on anteroconid of ml ; metatarsals III > IV > II » V > I. 



Description 



Tail subequal to or slightly longer than head and body (see Table 1 



Table 1 External and cranial measurements of Chibchanomys trichotis 

 and C. orcesi. Dimensions given as mean, plus or minus standard 

 deviation, followed by range, with sample size in parentheses. 





C. trichotis 



C. trichotis 



C. trichotis 



C. orcesi 





Venezuela 



Colombia 



Peru 



Ecuador 



Head and body 



113.5 ±5.50 







105 ±1.63 



length 



105-120(4) 



125(1) 



102(1) 



103-107 (3) 



Tail length 



126.8 ± 7.36 







113.3 ± 6.18 





115-133(4) 



131(1) 



123(1) 



108-122(3) 



Hindfoot length 



31.8 ±1.09 







22 ±2.16 





30-33 (4) 



30, 33 (2) 



31(1) 



19-24(3) 



Ear length 



7.5 ±1.5 







11.5 ±1.87 





6-10 (4) 



8(1) 



6(1) 



9.5-14(3) 



Weight (in grams) 



- 



- 



- 



37 + 2.83 

 35^1 (3) 



Ratio of tail 



1.12 ±0.02 







1.08 ±0.06 



length to head 



1.10-1.15(4) 



1.05(1) 



1.21(1) 



1.02-1.16(3) 



and body length 











Ratio of tail 



4.9 ±0.12 









length to condylo- 



4.7-5.0 (4) 



5.1(1) 



5.2(1) 



4.3, 4.7 (2) 



incisive length 











Ratio of hindfoot 



0.28 ± 0.00 







0.21 ±0.02 



length to head 



0.28-0.29 (4) 



0.26(1) 



0.30(1) 



0.18-0.23 (3) 



and body length 











Condyloincisive 



25.7 ± 1.01 









length 



24.3-26.9 (4) 



25.9(1) 



23.8(1) 



23.0, 24.6 (2) 



Diastema Length 



6.3 ±0.54 



- 





5.3 ± 0.29 





5.7-7.0 (3) 





5.7(1) 



5.0-5.7 (3) 



Length of upper 



4.4 ± 0.08 







4.2 ± 0.05 



molars 



4.3-L5 (3) 



4.4(1) 



4.2(1) 



4.1-4.2(3) 



Incisive foramina 



5.0 ±0.27 







4.5 ± 0.09 



length 



4.6-5.3 (4) 



5.1(1) 



4.5(1) 



4.4-4.6 (3) 



Breadth of 



1.2 ±0.11 







1.4 ±0.05 



incisor tips 



1.0-1.3(4) 



cl.2, 1.3(2) 



1.0(1) 



1.4-1.5(3) 



Breadth of incisive 



1.9±0.15 







2.1 ±0.09 



foramina 



1.7-2.1 (4) 



2.4(1) 



1.9(1) 



2.0-2.2 (3) 



Breadth of 



3.1 ±0.29 







2.2 ± 0.08 



palatal bridge 



2.7-3.4 (3) 



- 



2.6(1) 



2.1-2.3(3) 



Nasal length 



9.0 ±0.41 







9.3 ±0.29 





8.5-9.5 (3) 



8.1(1) 



8.5(1) 



8.9-9.6 (3) 



Nasal breadth 



3.0 ± 0.05 







3.2 ± 0.05 





2.9-3.0 (4) 



3.0(1) 



2.8(1) 



3.1-3.2(3) 



Interorbital breadth 



4.7 ±0.13 







4.6 ± 0.08 





4.5-4.8 (4) 



4.9(1) 



4.3(1) 



4.5-4.7 (3) 



Zygomatic breadth 



13.4 ±0.66 











12.3-14.1 (4) 



cl3.9(l) 



11.7(1) 



cl2.8(l) 



Braincase breadth 



13.4 ±0.27 











13.0-13.7(4) 



13.8(1) 



12.4(1) 



1.9, 12.0(2) 



Ratio of inter- 



0.35 ±0.02 









orbital breadth to 



0.33-0.37 (4) 



0.36(1) 



0.35(1) 



0.38, 0.39 (2) 



braincase breadth 











Breadth of 



1.1 ±0.05 







1.1 ±0 



zygomatic plate 



1.0-1.1 (4) 



1.0, 1.2(2) 



1.0(1) 



1.1(3) 



Breadth of first 



1.6 ±0.05 







1.3 ±0.05 



upper molar 



1.5-1.6(3) 



1.5(1) 



1.4(1) 



1.3-1.4(3) 



Height of upper 



4.6 ±0.33 







4.3-4.5 (3) 



incisor 



4.1-5.0(4) 



5.3(1) 



3.9(1) 



4.4 ± 0.08 



Depth of upper 



1.3 ±0.12 







1.2-1.3(3) 



incisor 



1.1-1.4(4) 



1.2(1) 



1.0(1) 



1.3 ±0.05 



Breadth across 



7.4 ±0.18 









occipital condyles 



7.2-7.6 (4) 



7.6(1) 



7.8(1) 



6.6, 6.7 (2) 



