Mammals from Bolivia. 227 



11. Neoctodon Simonsi, Tlios. 

 P. Z. S. 1902 (Feb. IStli). Abstract in ' Nature.' 



3 c?, 2 ? . Oruro, 3700 m. 

 c? ? . Challapata, 3800 m. 



2 c?, 2 ? . Livicliuco, 4500 m. 

 ? . Potosi, 4400 m. 



This handsome Neotoma-Wke animal, whose grey colour, 

 snowy-wbite belly, and bushy tail give it an exceedingly 

 striking appearance, has been described elsewliere. it is one 

 of the most interesting discoveries made by Mr. Simons. 



12. Cteyiomys opimus, Wagn. 



3 (J, 6 ?. Oruro, 3700 m. 

 (^, 3 ? . Challapata, 3750 m. 

 c?,2 ?. Pampa Aullaga, 3800 m. 

 i,^ ? . Potosi, 4300 m. 



c?. Livichuco, 4500 m. (" nigriceps''^). 



Tiiis species is evidently the common Tuco-Tuco of all the 

 region covered by the present collection, and it also goes 

 northwards to Lake Titicaca, while in Atacama and Tarapac^ 

 several of the forms described by Philippi are probably refer- 

 able to it. 



The species is a variable one as to colour, specimens from 

 the same locality showing a considerable range of variation 

 in the depth and tone of the yellow, which may be either 

 more buffy or more drab. The latter will perhaps prove 

 characteristic of the females. 



In addition, one specimen, that from Livichuco, is coloured 

 absolutely as in my C. o. m'griceps, originally from Titiri, 

 W. of Titicaca. Unfortunately no other Livichuco examples 

 were obtained, and I am therefore unable to express an 

 opinion as to whether this dark form, whose skull is indistin- 

 guishable from that of C. opimus, is there locally constant, as 

 at Titiri. The distribution is very curious, as the two places 

 are separated by regions inhabited by true opimus, a fact 

 which suggests that niyriceps may be only a " plumbeous 

 phase " of opimus, as occurs in the Geomyidse. But the 

 identity of the four Titiri specimens inter se is against this, 

 and the solution of the problem must therefore await further 

 material. 



In old skulls of this species the peculiar additional process 

 external to the condyle of the lower jaw (for which the name 

 of ectocondylar process might be used) is particularly well 

 developed. When the mandible is at its most posterior 

 position during the fore-and-aft motion this process articulates 

 with, or at least impinges on, the front face of the bony 



