482 RODENTIA 



Habrocoma} — Lower molars more complex than the upper; 

 ears large ; and fur extremely soft. Two Bolivian species. 



Schizodon.' 1 — One species, inhabiting elevated spots in the 

 Southern Ancles, and characterised by the enamel-folds of the upper 

 molars meeting in the middle line. The external characters are 

 much the same as in Ctenomys, but the ears are larger and the claws 

 shorter. 



Ctenomys? — Incisors broad ; molars rootless, with kidney-shaped 

 crowns ; last molar small and cylindrical ; eyes and ears very 

 small ; claws larger than the toes. Some four species. Fossil 

 remains are common in the Pleistocene of Buenos Ayres and the 

 cavern-deposits of Brazil. Habits fossorial. 



Spalacojnts. 4 — Bepresented by two Chilian species, distinguished 

 from the preceding genus by the rudimentary ears. These rodents 

 store up magazines of food in their burrows. 



Petromys. 5 — The South African P. typicus is closely allied to 

 Spalacopus, but differs by its harsh fur, the shortness of the pollex, 

 and the somewhat bushy tail. The teeth are semi-rooted, with 

 single inner and outer enamel-folds, nearly meeting in the middle. 



Subfamily Eehinomyinse. — Molars semi-rooted or rootless, with 

 deep and curved enamel-folds ; fur more or less harsh, frequently 

 mixed with spines ; tail generally long. One Ethiopian genus, and 

 the remaining nine or so Neotropical. Many of the species are 

 of large size, some being arboreal and others aquatic. 



Myopotaimis. 6 — Incisors very large ; molars with two internal 

 and two external enamel-folds in the upper, and three internal and 

 one external in the lower jaw, last molar the largest ; ears moder- 

 ate ; tail about two-thirds the length of the head and body, scaly, 

 and sparsely haired ; hind feet webbed ; five digits. Vertebra? : 

 C 7, D 13, L 6, S 4, C 25. The well-known Coypu (M. coypu), the 

 only existing representative of this genus, is one of the largest 

 living members of the order, and attains a length of about 2 feet. 

 It is common in South America, living in burrows near Avater, and 

 feeding on aquatic plants. Fossil remains of the genus occur in the 

 caverns of Brazil, as well as in the Tertiaries of Argentina. 



( 'djiromys. 7 — This genus comprises arboreal forms from the West 

 Indies allied to the Coypu, but, according to Dr. G. E. Dobson, 

 showing signs of affinity with the Hystricidce. The incisors are 

 smaller than in the Coypu, and the upper molars have one internal 



' \Yaterhouse, Proc. Zool. Soc. 1837, p. 30. Amended from Abrocoum. 



2 Waterhouse, Proc. Zool. Soc. 1841, p. 91. 



:i De Blainville, Bull. Soc. Philom. 1826, p. 62. 



4 Wagler, ibid. p. 1219. 



5 Andrew Smith, S. African Quart. Jowrn. vol. ii. p. 2 (1831). 



I! Geoffroy, Ann. d/u Musium, vol. vi. p. 81 (1805). 



7 Desmarest, Mem. Soc. d'Hist. Nat. vol. i. p. 44 (1822). 



