594 



OBSERVATIONS OK THE RODENTIA. 



The molar teeth of Spalax [n and o) possess the same ir- 

 regular-formed and imperfect fangs as are found in old speci- 

 mens of Arvicola and Ondatra, but apparently they have 

 these fangs at an early age, and thus evince approach, as 

 regards the teeth, to the Muridae. The cranium in the Arvi- 

 colida is usually rather broad, and proportionately shorter 

 than in the Muridce ; in Ondatra, Arvicola, and Lemmus, 



70 



Skull and lower jaw of Ondatra zibethica. 



(k) molar tooth of an aged specimen of Ondatra. (J) section of incisor tooth of Arvicola. 



[m) section of incisor of Mus. (n) and (o) molar teeth of Spalax. 



the temporal bone is produced anteriorly and laterally, and 

 in some of the species forms an angle, as in Arvicola am- 



