152 NATURAL HISTORY. 



respects the skull resembles that of Arctomys, but it has the same contraction between the orbits 

 as Ischyromys and Fiber. The incisor teeth are separated, and Professor Cope believes that the animal 

 had only three molars on each side in each jaw. A still more doubtful member of the family is 

 Professor Cope's genus Grymnoptycbtu, which includes four species, all said to be from the " Tertiary 

 of the Plains." In this genus there are five molars above and four below on each side, as in Ischyromys 

 and the Sciuridse ; but these teeth show two crescents on the inner side in the upper, on the outer 

 side in the lower jaw, and each crescent gives origin to a cross-ridge running to the opposite margin of 

 the tooth. 



The CASTORID.E, including at present only a single species common to the northern parts of both 

 hemispheres, are represented by several peculiar fossil forms. Remains of the Common Beaver 

 (Castor fiber} are not uncommon in peat bogs and other late superficial deposits both in Europe and 

 America ; and, according to Sir R. Owen, in association with those of the Rhinoceros, Mammoth, 

 and Mastodon, even in the Fluvio-marine Crag (Newer Pliocene) of Norfolk. In Belgium its bones 

 have been found in caves. Among the Mammals from the Upper Tertiaries of the Sivalik Hills, 

 Messrs. Falconer and Cautley record a Beaver distinct from the existing species, although nearly allied 

 to it. The skull of a great Beaver, one-fifth larger than that of the living species, was obtained many 

 years ago by M. Fischer from sandy deposits on the shores of the Sea of Azov, and, as it differed in 

 some peculiarities of the teeth from Castor fiber, was described by him as constituting a distinct genus 

 under the name of Troyontfterium Cuvieri. It is now regarded as a true Beaver, and named Ctutpr 

 Trogontlwrium. The British species, described and figured by Sir R. Owen from the Norfolk 

 Forest bed under the name of Trogontherium C^(v^er^, is, however, quite distinct, and belongs to the 

 genus Diobroticus, characterised by having the third upper and first lower molar teeth with four 

 enamel folds, and the rest only with two, most of the folds soon becoming isolated as the teeth 

 wear down. This animal must have been nearly twice the size of the European Beaver. 



At a still earlier period namely, in the Miocene the family Castoridse was represented, both 

 in Europe and America, by some small species, nearly agreeing with the Beavers in dentition, but 

 differing in the characters of certain bones of the skull. These form the genus Steneofiber. The 

 largest (S. viciacensis), from the Miocene of the Allier, was about half the size of the Beaver ; another 

 (S. sansaniensis), from the fresh-water limestone of Sansan, was about as large as a Rat; an 

 American species (S. nebrascensis), from the " Bad Lands " of Dakota, was rather smaller than a 

 Marmot, and presented some resemblance to the Agoutis in the characters of the teeth ; and a fourth 

 species (S. pansus) occurs in the Santa Fe marls. Eucastor tortus, a species rather smaller than a 

 Marmot, is described by Dr. Leidy as very nearly related to the Beaver. Its remains were found in 

 loose sands of the Niobrara River, Wyoming. Chalicomys and Palceomys are genera doubtfully placed 

 here. Their species occur in the Miocene and Pliocene of Europe. 



Some bones of a gigantic Rodent, indicating an animal as large as a full-grown Black Bear, 

 obtained from Quaternary and Alluvial deposits of various parts of the United States, have been 

 described under the name of Castoroides ohioensis, Mr. J. W. Foster, its first describer, having an 

 idea that it was a great Beaver. It has generally been known as the " Fossil Beaver " of North 

 America, but several authors have entertained doubts of the coi-rectness of this designation, and Mr. Allen 

 has lately made it the type of a special family, CASTOROIDID.E, which he regards as most nearly related 

 to the Chinchillidse. In the general aspect of the skull it resembles the Beaver, but in several 

 details of structure approaches the Viscacha ; while the structure of the molar teeth, which consist 

 of a series of plates of dentine, completely eclosed by enamel, and held together by a thin coating of 

 cement, occurs elsewhere only in the Chinchillidse, and in the last molar of the Capybara. 



Dormice as well as Squirrels disported themselves in the Tertiary woods and thickets of Europe, 

 and remains of several species of MYOXID^E occur in various deposits in France, Switzerland, and 

 elsewhere, from the Upper Eocene onwards. Myoxus glis, the Garden Dormouse, has been identified 

 with some doubt from the caves of Lunel Viel ; and this is also probably the species occurring in the 

 Belgian bone-caves, and described as Myoxus prisons by Dr. Schmerling. A species a little larger 

 than the Dormouse occurs in Russian caves, and has received the name of Myoxus fossilis from 

 M. Fischer ; and the most striking species of all is also a Post- Pliocene form, namely, the gigantic 

 Dormouse of Malta (M. melitensis). This animal, which seems to have been about the size of a 



