953 



MURID.E. 



951 



F. Cuvier commences tliia ' Memoir ' with observing that his 

 attention had been particularly directed to the Sodentia, with a view 

 of arriving at a natural classification of the numerous species com- 

 posing that order, among which considerable confusion had hitherto 

 prevailed, particularly in the genera Dipus and Gerbillus, the relations 

 of which to other allied groups had been but very imperfectly under- 

 stood by previous writers. The species included in the genus Dipus 

 had been formed by M. Lichtenstein into three divisions, which are 

 distinguished by the absence and number of rudimentary toes upon 

 the hind feet. In the first section are placed those with three toes, 

 all perfectly formed ; in the second, those with four, one of which is 

 rudimentary ; and in the third, those with five, two of these being 

 rudimentary. F. Cuvier states that he is unacquainted with the 

 second division of M. Lichtenstein ; but in the examination of the 

 species belonging to the first, in addition to the absence of rudimentary 

 toes, he finda that they are also distinguished from those of the third 

 by the form of the teeth and the osteological characters of the head. 

 These points of difference he considers of sufficient importance to 

 justify a distinct genus for the Jerboas with five toes, adopting the 

 name Alactaga, given by Pallas to a species, as the common generic 

 appellation. F. Cuvier remarks that the three principal toes of the 

 Alactaga,", as well as the three only toes of the Jerboas, are articulated 

 to a single metatarsal bone, and that the two rudimentary toes of the 

 first genus have each their metatarsal bone ; whence it results that 

 the penultimate segment of the foot is composed of three bones in 

 the Alactagas, and of one only in the Jerboas. The incisors of the 

 Alactagas are simple, whilst those in the upper jaw of the Jerboas are 

 divided longitudinally by a furrow. The molars of the latter genus 

 are complicated in form, and but little resemble those of the former. 

 They are four in number in the upper jaw, and three in the lower ; 

 but the first in the upper is a small rudimentary tooth, which probably 

 disappears hi aged individuals. After a detailed account of the struc- 

 ture of the grinding teeth, F. Cuvier observes that the general 

 structure of the head of the Alactagas and Jerboas is evidently the 

 same, and is characterised by the large size of the cranium, the short- 

 ness of the muzzle, and, above all, by the magnitude of the suborbital 

 foramina. The cranium of the Jerboa is distinguished by its great 

 breadth posteriorly, resulting from the enormous development of the 

 tympanic bone, which extends beyond the occipital posteriorly and 

 laterally, as far as the zygomatic arch, which is by no means the case 

 in the Alactagas, where all the osseous parts of the ear are of moderate 

 dimensions. Another differential character between the two genera 

 is presented by the maxillary arch, which circumscribes externally 

 the suborbital foramina, and which, in the Alactagas, may be said to 

 be linear, presenting a very limited surface for the attachment of 

 muscles. He then notes a difference in the relative development of 

 the jaws, the lower being comparatively much shorter in the Alactagas 

 than in the Jerboas. Having described a new species of Alactaga, a 

 native of Barbary, under the name of Alactaga arundinis, F. Cuvier 

 proceeds to consider the characters and affinities of the genera Ger 

 tiillua and Meriynca, and enters into a critical examination of all the 

 species referred to that group. To these he adds another species, the 

 habits of which he describes, and to which he gives the name of 

 Gerbillui Burtoni. The cnecies he includes are : ], Gerbillus 



Burlmi. The detailed descriptions of these are given in the 'Trausac- 

 ions of the Zoological Society,' in which will also be found F. Cuvier's 

 'iews with ragard to the affinities of the Gerbillas and Alactagas to 

 ,he Jerboas, and which lead him to the conclusion that the Gerbillas 

 mve a much nearer affinity to the Muridce. 



(jcrliltiu Burton!. 



ti'ocvi, Syn. ; Dipui Gerbillui, Meriones quo.drimaculo.tug, Ehvenberg. 

 2, Gerbillus Pyramidum, Syn. ; Dipus Pyramidum, Geoff. ; Merionet 

 robuitut, RUpp. 3. Gerbillas pyjargus, Syn. ; Mcriones Gerbillus 

 Riipp. 4. Gerbillui Indicus, Syn.; Dipus Indicus, Hardwicke. 6 

 'liu Africamu, Syn.; Mcriones Schkijelii, Smutz ; Gerbillus Afra. 

 Gray. 6. Gerbillui brevicaudatiw. 7. Gerbillus Otaria. 8, Gerbillus 



Cranium and Teeth of Gerlillus Burtoni. 



a, skull, profile ; I, same, seen from above ; c, same, seen from below ; d, e, 

 teeth of same. 



General Hardwicke gives the following interesting account of his 

 Dipus Indicus : " These animals are very numerous about cultivated 

 lands, and particularly destructive to wheat and barley crops, of 

 which they lay up considerable hoards in spacious burrows near the 

 scenes of their plunder. They cut the culms of the ripening corn 

 just beneath the ears, and convey them thus entire to one common 

 subterraneous repository, which when filled they carefully close, and 

 do not open for use till supplies abroad b -ocine distant and scarce. 



Dark-Handed Jerboa. 



Grain of all kinds is their favourite food ; but in default of this they 

 have recourse to the roots of grass and other vegetables. About the 

 close of day they issue from their burrows, and traverse the plains in 

 all directions to a considerable distance ; they run fast, but oftener 

 leap, making bounds of four or five yards at a time, carrying the tail 

 extended in a horizontal direction. When eating they sit on their 

 hind legs likeja squirrel, holding the food between their fore feet 



