590 



]\Ir. 0. Thomn.s on 



T'/pr. Adult female, permanent dentition in place. B.M. 

 ro. 5. 2. 5. 1\). Collected 24t]i November, 190-i, by S. Briccno. 

 Two specimens. An imperfect specimen from Bogota also 

 apparently the same. 



"Eyes blue. ^Makes a nest underground, with two 

 exits/^— S. B. 



The Pacas fall into two groups, those of the mountains and 

 those of the plains. The former are comjiaratively long ami 

 thickly haired and darker coloured, and liave the sole-pads 

 distinct and profusely granulated ; so far as is yet known, 

 they are confined to the mountains of N.W. S. America. 

 On the other hand, the lowland Pacas, ranging from Panama 

 to South Brazil, are more sparsely covered with shorter hair, 

 are ])aler in colour, brown or rufous, and their foot-pads are 

 smoother, especially posteriorly, and less sharply defined from 

 the general surface of the sole. 



I'o the lowland group belong the forms described as j>aca, 

 Linn., fulvus, F. Cuv., siibniger, F. Cuv.*, and virgatus, 

 Bangs, while to the highland series should be referred Taczan- 

 owskiij Stolzmann, and the ])resent new form, which may 

 be identified by its small size and very small bullre. The 

 animal described by Gervais, from the skull only, as .9«^^npy/.f, 

 from Colombia, cannot be identified, and the type is no longer 

 to be found in the Paris Museum. It may have been a 

 female of either paca or Taczanowskii\ but, no mention being 

 made of its size being specially small, it is not likely to have 

 been the present species. 



Mesomys, Wagn. 



At last I cim able definitely to identify the genus Mesomys 

 of Wagner, which has been a puzzle to zoologists for half a 

 century. Founded originally on a specimen which had lost 

 its tail, an accident of most common occurrence in the group, 

 tailless specimens of several other groups have been assigned 

 to it, and all sorts of erroneous conclusions have been 

 published about it on this account. Of late years, as in 

 Dr. Allen's paper f on Eclnmys and Proechimys, it has been 

 looked upon as probably synonymous with the former. 



* Tv]ie locality Tobago. But I am informed by that excellent 

 iiatuialist Mr. H. Caiacciolo that the Paca i.* not iudipenous to Tobapo, 

 and tliat it was probably introduced tliere from Trinidad. 



t ]Jull. Am. Mils. K.'ll. xii. p. 2o7 (1899). Trouess^irt, in the recent 

 Supplement to his ' Conspectus,' .seems to have misunderstood the gist of 

 Dr. Allen's paper, as he uses Echinnjs for the cristatus group and Eunj 

 zijgoynatomys for xpinoms. ]?ut it is quite clear, as Dr. Allen as shown, 

 that Echimys should be used for the latter and Loncheres for the former. 



