XV CASTOREIN AND ITS USES 469 
forefathers. The Rev. Edward Topsell observed that “for giving 
great ease unto the gowt the skinnes of beavers burned with drie 
oynions ” are excellent. Castorein as a drug, if not in actual use, 
has quite recently been a part of the pharmacopoeia. It is 
derived from the anal glands common to this and other Rodents, 
and indeed many other mammals. 
A large extinct form of Beaver is 7rogontherium,' found in the 
“ Forest-bed ” of Cromer. The skull is about one-fourth longer 
than that of Castor. It has a less inflated bulla, and shghtly more 
pronounced postorbital processes than Castor. The third molar 
(fourth grinding tooth) is relatively larger than in Castor, and has 
a rather more folded crown. The foramen magnum is more 
triangular. 
Fam. 4. Haplodontidae.—A separate family seems to be re- 
quired for the genus Haplodon, whose characters will therefore be 
merged with those of its family. It is to be distinguished from 
most other Squirrel-like creatures by the fact that there is no post- 
orbital process to the frontal. The molar teeth are five in the 
upper and four in the lower jaw. The Sewellel, H. rufus, like 
the other species of the genus (H. major), is found in North 
America west of the Rocky Mountains. It has the habit of the 
Prairie-marmot, and has a short tail, only moderately long ears, 
and five-toed feet. Tullberg is of opinion that this animal nearly 
represents the ancestral form of the Squirrel tribe. 
SECTION 2. MyYOMORPHA. 
This subdivision of the Rodents contains, according to Mr. 
Thomas’s recent estimate, no less than 102 genera. It is there- 
fore obviously impossible to do more than refer to some of the 
more interesting of these. This group is again divided into the 
following families -— 
(1) .Ghiridae, including the Dormice. 
(2) Muridae, the Rats, Mice, Gerbilles, Australian Water-rats, 
Hamster. 
(3) Bathyergidae, Cape Mole, etc. 
(4) Spalacidae, Bamboo Rats. 
1. T. Newton, Trans. Zool. Soc. xiii. 1892, p. 165. 
2 Proc. Zool. Soc. 1896, p. 1016. 
