MILLER AND GIDLEYI SUPERGENERIC GROUPS OF RODENTS 445 



Subfamily Atherurinae. — Base of upper zygomatic root over anterior 

 extremity of toothrow; cheekteeth subhypsodont, with well developed 

 roots; sacral vertebrae 3. 



Atherurus, Trichijs; Recent; Malay region. 



Family ERETHIZOXTIDAE 



Like the Hystricidae but: Mandibular rami with conspicuous post- 

 SJ^nphyseal buttresses which prevent movement at the symphysis; 

 lower border of angular process folded inward; cheekteeth subhypso- 

 dont, flat crowned, with reduced-heptamerous enamel pattern char- 

 acterized by narrow ridges and wide reentrant spaces, the spaces on the 

 paramere tending to become transformed into pits (parallels: Funis- 

 ciurus, Anomaluridae) . Upper zygomatic root over anterior part of 

 toothrow; feet noticeably modified for arboreal life. 



New World porcupines except Chaetomys: Oligocene to Recent. 

 Oligocene of Egypt?^ Extinct South American genera: Asteromys, 

 Eosteiromys, Parasteiromys, Steiromys. 



Family ECHIMYIDAE 



Like the Erethizontidae but lower border of angular process usually 

 with no evident infolding, feet usually not modified for arboreal life, and 

 adult cheekteeth with narrow reentrant folds; cheekteeth varying from 

 brachydont to ever-growing, the structure when hypsodont not multi- 

 laminar. 



Subfamily Echimyinae.—Fo^'&oviaX specialization usually absent; 

 skull and cheekteeth showing great variety of form ; enamel pattern not 

 simplified to a ring with an infold on one or each side. 



Tropical America; Miocene to Recent. Spiny-rats (provisionally 

 including Chaetomys), Hutias {Capromys, Plagiodontia) , etc.; also many 

 extinct genera, among them Acaremys, Boromys, Brotomys, Colpostemma, 

 Eocardia (parallel: Issiodoromys), Eododon, Graphimys, Gyrignophus, 

 Haplostropha, Heteropsomys, Homopsomys, Isolobodon, Prospaniomys, 

 Protadelphomys, Protacaremys, Sciamys, Scleromys, Spaniomys, Sticho- 

 mys, Strophostephanus, Tribodon. It is probable that this group needs 

 subdividing. 



Subfamily Octodontinae. — FoSsorial specialization usually present; 

 cheekteeth, except in earliest known genera, with enamel pattern com- 

 pletely simplified to a ring with an infold on one or each side (parallel : 

 Ctenodactylidae) . 



South America; Oligocene to Recent. Recent genera: Ctenomys, 

 Octodon, Octodontomys, Spalacopus. Among the fossil genera are: Ceph- 

 alomys, Dicoelophorus, Eucoelophorus, Litodontomys, Neophanomys, 

 Palaeododon, Phtoramys, Pithanotomys, Plataeomys, Scotomys. 



* The genera Phiomys and Metaphiomys, based on lower jaws and teeth, have 

 no characters by which they can at present be referred to any other family. 



