144 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



MICROSCIURUS ISTHMIUS VIVATUS Goldman 



Mount Pirre Pygmy Squirrel 



[Plate 30, figs. I, la] 



Microsciurus isthmius vivatus Goldman, Smiths. Misc. Coll., Vol. 60, No. 2, 

 p. 4, September 20, 1912. Type from near Cana, eastern Panama (alti- 

 tude 3,500 feet). 



Comparatively little is known of the relationships of pygmy- 

 squirrels, most of the known forms being currently regarded as full 

 species based on scant material from few localities. It was, there- 

 fore, with considerable interest that I noted the occurrence of two 

 very distinct forms in close proximity on the Cana slope of the Pirre 

 Mountains near the Colombian frontier. One of them proved to be 

 Microsciurus alfari venustulus, previously known only from farther 

 west, and the other an apparently new geographic race of M. isthmius 

 whose general known range is in the valley of the Atrato River and 

 the coast region of Colombia. Since M. i. vivatus, the new form, 

 inhabits these mountains at 3,500 feet altitude, while M. a. venustulus 

 was taken only 1,500 feet lower down on the steep slope, both will 

 probably be found at the same elevations. M. i. vivatus is dis- 

 tinguished from M. isthmius isthmius by paler upperparts and 

 orange buffy instead of deep ferruginous underparts. Anthony 

 (1916, p. 366) records specimens of M. i. vivatus from 2,650 feet 

 altitude near the village of Tacarcuna, which closely resemble speci- 

 mens from the type locality, but have slightly richer-colored under- 

 parts. The examples of M. i. vivatus were obtained by me while . 

 hunting birds. They were all found among the lower branches or on 

 the trunks of trees, where they were inconspicuous owing to masses 

 of dense overhanging vegetation in the dimly lighted forest. In this 

 forest, fog enshrouded during much of the time, one of these tiny 

 squirrels moving along a tree trunk may easily be mistaken for one 

 of the common Dendrocolaptine or Formicariinine birds of the 

 region. 



Specimens examined: Cana (type locality), 3; Mount Tacar- 

 cuna, 3. 1 



Genus SYNTHEOSCIURUS Bangs. Pygmy Squirrels 

 In this as yet monotypic genus of small tree squirrels an unusual 

 departure in dental details is exhibited. The upper incisors are very 

 slender and project outward and the outer surfaces, smooth in 

 Sciurus and Microsciurus, each bear a longitudinal median groove. 



Collection Amer. Mus. Nat. Hist. 



