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 Eodents, 

 and indeed many other mammals. 



A large extinct form of Beaver is Trogontherium, 1 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 slightly 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. rv/us, like 

 the other species of the genus (ff. major}, is found in North 

 America west of the Eocky 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. MYOMOEPHA. 



This subdivision of the Eodents contains, according to Mr. 

 Thomas's recent estimate, 2 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) Gliridae, including the Dormice. 



(2) Muridae, the Eats, Mice, Gerbilles, Australian Water-rats, 

 Hamster. 



(3) Bathyergidae, Cape Mole, etc. 



(4) Spalacidae, Bamboo Eats. 



1 E. T. Newton, Trans. Zool. Soc. xiii. 1892, p. 165. 

 2 Proc. Zool. Soc. 1896, p. 1016. 



