108—4 INDIAN TERTIARY AND POST-TERTIARY VERTEBRATA. 
bility distinct. In all the recent forms the molars are relatively wider than those of 
the fossil. 
It appears, therefore, that the Siwalik Uhisomys, whether it comprehends one or 
more species, is probably distinct from any of the living forms ; and it may accord- 
ingl}^ retain the provisional name, B,. sivalensis. The relatively wider molars and the 
larger size of the incisors of the existing forms as compared with those of the fcxssil 
seem to indicate that specialization has tended to the production of these 
characters. 
Distribution. — Remains of the Siwalik Bhizomys have been obtained from the 
typical Siwalik Hills and the Punjab. 
Family III.: RYSTBICIDjE. 
Dental Characters. — According to the late Mr. E. R. Alston^ the living members 
of the Uystricidw present the following dental characters, viz. : 
A. Sphingurin.®. Cheek-teeth rooted. Nearctic and Neotropical. 
Choelomjs, Gray. Upper cheek-teeth each divided into three lobes, of which the first 
' and last have deep single enamel-folds ; lower teeth with an external and two 
internal folds. _ 
Synetheres'^ F. Cuv. Cheek-teeth like Chcelomys, but with two lobes only : equal in 
size. 'I 
Erefhizo7i, F. Cuv. Cheek-teeth like Synetheres, but anterior larger than posterior. 
B. Hystricin^. Cheek-teeth, semi-rooted, Palaearctic, Indian, and Ethiopian. 
Atherimi, Cuv. Upper cheek-teeth with one internal, and three or four external 
enamel-folds, the latter soon separated into enamel-loops : lower teeth similar 
but reversed. 
Hystrix, Linn. Teeth as in Alherura. 
It thus appears that while the American porcupines can be distinguished palte- 
ontologically from those of the Old World, the genera A and Hystrix cannot be 
distinfruished bv characters usually available in the case of fossils. The cheek-teeth 
of Dasyprocta 'uro. also very similar to those of the smaller jtorcupinos ; but none, of 
the species of that genus, or Atheriira., attain such a large size as some species of 
Hystrix. 
Genus: HYSTRIX, Linn. 
Distribution, and number of fossil syiecies. — The genus is contined to the Old 
World at the jiresent day; but in former times it apparently ranged into America, if 
Hystrix venusta be rightly determined. It will be unnecessary to give a list of the 
existing species ; but it may be mentioned that the South European and African 
//. cristata, Ijinn., and the Indian H. hirsutirostris,^ Brandt, are the largest forms. 
The earliest recorded occurrence of a porcupine, or allied form, is in the “ Quercy 
Phosphorites,” from which deposits a fragment of a mandible has been described by 
Dr. FilhoP under the name of H. (?J lamandini. Besides this there is the so-called 
1 Op. cii. 2 Syn. Cercolaben, Brandt. Sphinguriis, F. Cuvier. 
3 Syn. IT. Sykes. 4 “ Phosphorites du Quercy ” (reprint) p. 49. 
