306 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1923 



The spider monkeys are remarkable for the highly developed pre- 

 hensile tail, which is constantly used as a fifth hand. They are 

 among the most perfectly arboreal of mammals and exhibit the great- 

 est agility in their movements throughout the tree tops. Numerous 

 species are known and the range of the genus extends northward 

 well into Mexico. The species most commonly exhibited in the park 

 is the gray spider monkey {Ateles geoffroyi). Various species of 

 squirrel monkeys and marmosets are shown from time to time. 



THE LEMURS 



Although several groups of lemurs are known from Africa and 

 the oriental region, the species included within the typical genus 

 Lemur, and known as " true lemurs," are confined to Madagascar 

 and neighboring islands. They have a foxlike face and muzzle and 

 a long tail. The numerous species are essentially arboreal and many 

 of them are strikingly colored. The mongoose lemur {Lemur 

 mongoz) is a noisy, gregarious species, noted for its agility in trees. 

 In addition to this species, the black lemur {Lemur macaco) and 

 the fulvous lemur {L. fulvus) are shown. 



THE GNAWING MAMMALS 



Among the gnawing mammals are included two very distinct 

 orders — the Rodentia and the Lagomorpha. The latter order is made 

 up of the hares, rabbits, and pikas, while all the other existing rodent- 

 like forms are members of the order Rodentia. The vast majority 

 of rodents are small creatures, like the mice, rats, and squirrels; but 

 the order includes some very sizable living animals — the porcupine, 

 beaver, and capybara, while an extinct South American member of 

 the group was as large as a hippopotamus. The most characteristic 

 features of the Rodentia are the complete absence of canine teeth and 

 the great development of the incisors which, owing to their per- 

 sistent growth and the presence of hard enamel chiefly on the an- 

 terior surface, are worn by use to a chisel-like edge. There is always 

 a considerable space on the jaw between these cutting teeth and the 

 molariform grinders. 



Until some special means for the exhibition of living examples of 

 the smaller rodents and lagomorphs can be devised, the collection 

 must be mainly restricted to the larger forms. The common gray 

 squirrel and the cottontail rabbit roam wild within the borders of 

 the park. Among the gray squirrels will be seen numerous black or 

 blackish examples. These are descendants of black squirrel stock in- 

 troduced in the park a number of years ago from southern Ontario. 



