1H80.] 



SPECIES OF REITHRODON. 



695 



what move strongly made. As the ears also in R. typicus are decidedly 

 longer than in B. cuniculoides, being 0-74 inch long as against 

 56, measured in each case from the base of the outer edge, and 

 the tarsi are shorter (I' 12 against 1-26 without the claws), I do not 

 think that at present we are justified in assuming the existence 

 of intermediate forms, though I have but little doubt that such will 

 yet be found to occur. I exhibit a drawing (fig. 3, p. 694) of 

 what remains of the skull of the type of B. f>/picus, which has only 

 recently been taken out of the skin, and therefore was not figured 

 with the others in the Zoology of the voyage of H.M.S. ' Beagle.' 



As to the localities from which specimens of this genus have been 

 obtained, I may mention that, besides the types of Waterhouse's 

 three species, the British Museum possesses a specimen in spirit 

 oi B. chinchilloides, obtained by the Antarctic Expedition of 1842 

 close to Cape Horn, and a skin of the same species collected 

 by Mr. T. Bridges in the province of Mendoza, Central Chili. 

 There is also a specimen of B. typicus recorded from Parana, La 

 Plata, by Burmeister '. 



As we have thus two specimens in spirit belonging to the genus 

 Beithrodon, besides a good series of Sigmodon and Ilesperonujs, I 

 have thought it worth while to examine and compare the alimentary 

 canals of specimens belonging to these genera. 



In the first place I exhibit a drawing (fig. 4) of the caecum 



Pig. 4. 



Crecum of licithrodon ahtoni 



of R. ahtoni ; it is of the natural size, and shows the shape 

 of the organ very well, la R. chinchilloides the caecum is very 



» Eeise durcli die La Plata-Staaten, p. 413 (1861). 



