406 Expedition to the 



out trees or bushes. As we followed the little pathway 

 towards Bon Homme we passed large tracts, to which the 

 labours of the sand rat* had given the aspect of a ploughed 



* Genus Pseudostoma.* Say. Cheek-pouches exterior to the mouth; 

 incisores naked, truncated; molares sixteen, destitute of radicles; crown 

 simple, oval; anterior ones double. 



Species, Pseudostoma bursaria. Body sub-cylindrical, covered with 

 reddish-brown hair, which is plumbeous at base; feet white, anterior nails 

 elongated, posterior ones short, and concave beneath. 



J\lus bursarius, (Shaw Trans. Lin. Soc. Lond. and Genl. Zoology.) 

 Body elongated, sub-cylindrical; hair reddish-brown, plumbeous at base; 

 beneath rather paler; cheek pouches capacious, covered with hair, both 

 within and without; vibrissa? numerous, slender, whitish; eyes black; ears 

 hardly promineat; feel five-toed, white; anterior pair robust, with large, 

 elongated, somewhat compressed nails, exposing the bone on the inner 

 side, middle nail much longest, then the fourth, then the second, then the 

 fifth, the first being very short; posterior feet slender, nails concave be- 

 neath, rounded at tip, the exterior one very small; tail short, hairy at base, 

 nearly naked towards the tip. 



This animal is congeneric with the Tucan of Hernandez, which Buffon 

 erroneously considers the same as the Talpha rubra Americana of Seba, 

 or Talpha rubra Lin., an animal which is however entirely out of the 

 question, and which, if we may be allowed to judge from Seba's figure, is 

 so far from having any specific affinity with the bursarius, that it cannot 

 now be regarded as co-ordinate with it. 



The late professor B. S. Barton, in his Medical and Physical Journal, 

 says, that a species of Jllus allied to the J\l. bursarius of Shaw, is common 

 in Georgia and Florida, that he examined a living specimen of this animal, 

 and was convinced, that it is no other than the Tucan of Hernandez, and 

 the Tuza or Tozan of Clavigero. He says nothing of its size, but on the 

 same page he remarks, that " another species of Mus, much larger than 

 the Tuza, inhabits west of the Mississippi about latitude 30°, of which 

 verv little is known." Dr. Barton was aware that the cheek pouches, in 

 the figures given by Shaw, are represented in an inverted position, but not 

 having seen specimens from the trans-Mississippi country, he was unac- 

 quainted with their specific identity with those of Canada, from which 

 those figures were drawn. In our zoological reports to Major Long, in the 

 year 1C19, the specimens which we found on the Missouri were recorded 

 under the name of bursarius of Shaw. Coxe, in his description of " Caro- 

 lana called Florida, and of the Meschacebe", in 1741, mentions a "rat 

 with a bag under its throat, wherein it conveys its young when forced to 



fly." 



Several other writers have noticed these animals, of whom Dr. Mitchell, 

 in Silliman's Journal, 1821, mentions the ideutity of specimens obtained 

 beyond Lake Superior, with the M. bursarius of Shaw. 



The animals belonging to this genus are distinguished by their volumi- 

 nous cheek-pouches, which are perfectly exterior to the mouth, from which 



* From -{ivSu, false; and a-Toy.*, a mouth, in allusion to the false mouths or 

 cheek-pouches. 



