RODENTIA. 151 



B. hottentottus, Less, and Garn., Voy. de la Coquille, pi. ii. 

 (The Hottentot Rat-Mole.) Smaller ; grey ; incisors smooth ; 

 hardly as large as a Rat. The 



GeomyS; Rafiii. PsEUDOSTOMA, Say. Ascomys, Lichten. 



Which have four compressed prismatic molars throughout; the 

 first double, the remaining three simple; the upper incisors furrowed 

 with a double groove in front ; five toes to each foot ; the three 

 middle anterior nails, that of the medius particularly, very long, 

 crooked, and trenchant. They are low animals, and have very deep 

 cheek-pouches, which open externally, enlarging the sides of the 

 head and neck in a singular manner. One species only is known, 

 G. biirsarius; Mus bur sarins, Shaw.(l) (The Canada Ham- 

 ster.) Size of a Rat;^fur of a reddish grey; tail naked, 

 and but half the length of the body. Inhabits deep burrows in 

 the interior of North America. 



DiPLOSTOMA, RaiBn. 



The Diplostomee are almost precisely similar to the Geomys, but 

 they have no tail. (2) 



These animals are also from North America. The species 

 before us is reddish, and ten inches in length. 



We now pass to larger Rodentia than those of which we 

 have hitherto spoken, but of which several still have well 

 defined clavicles. Of this number is the 



Castor, Lin. 



The Beavers are distinguished from all other Rodentia by their 

 horizontally flattened tail, ^'hich is nearly of an oval form, and 

 covered with scales. They have five toes to each foot : those of the 

 hinder ones are connected by membranesj and that next to the thumb 

 has a double and oblique nail. Their grinders, to the number of 

 four throughout, and with flat crowns, appear as if formed of a 

 doubled bony fillet, or so as to show one sloping edge at the internal 



CI) The figures of this animal, first published Trans. Lin. Soc. Vol. Y, jdI. viii, 

 and Shaw, Vol. II, part I, pi. 138, represent it with the internal skin of the 

 cheek-pouches tiu-ned inside out, as though it had two sacs to the sides of the 

 head. There is nothing Hke it in nature. It is well represented, Acad. Berhn, 

 1822 and 1823, pi. ii. 



(2) M. llafinesque describes them as having only four toes to each foot. The 

 European species has five, like the Geomys. 



