Messrs. Say and Ord on Sigmodon hispidum. 



bulletin, appeared to coincide in the opinion that the animal was 

 a Mi/oxus, and not a Mus. 



That it was neither a Myoxus nor a Mus^ will now he evident 

 from the figures of its teeth. When we first commenced an ex- 

 amination of its teeth, we were astonished to find in the grinding 

 surfaces of the molares, a close approximation to those of Arvi' 

 cola; but the discovery of radicles, precluded our referring it to 

 that genus. 



Although we are aware that the multiplication of genera has 

 become an evil, yet we have ventured to found a genus on our 

 animal, from our inability to class it under any of the genera of 

 the systems. 



Plate X. Neotoma Floridana, 

 Fig. 1. Profile view of the Jaws, magnified. 



2. Lower Jaw left side, with the alveolar process removed, in 



order to exhibit the roots of the teeth ; natural size. 



3. Molaresof the upper jaw, leftside, magnified. 



4. Molaresof the lower jaw, left side, magnified. 



Art. XXXIII. Description of a new species of Mammalia, 

 whereon a genus is proposed to be founded. By Mr. 

 T. Say and Mr, G. Ord.* 



Order. Glires. 

 Genus. Sigmodon. 



Essential Character. 

 Molares in each jaw six, subequal, with radicles, and with very 

 profound, alternate folds towards the summit. 



Natural Character. 



incisores. 



molares. 

 i2 incisores. 

 !6 molares. 



Teeth 16 



* From the Journ. Acad. Nat. Sc. Phil. 



