446 Arvicola Nuttalli. 



those above given, there can be no reasonable doubt left but 

 that the true atomic weight of mercury is 100 ; (hydrogen basis ;) 

 and although these would not of themselves be sufficient to es- 

 tablish this fact, yet Mr. A. is fairly entitled to the credit of 

 having shown that to be highly probable, which Dr. Thompson's 

 investigations have rendered certain. — Very respectfully, yours, 



J. B. 



New York, February 38th, 1833. 



ARVICOLA NUTTALLI. 



Description of a new species of quadruped of the genus Arvicola, of 

 Lacepede, or Hypudceus, of Illiger. — By R. Harlan, M. D. 



Arvicola JVuttaUi. — Fawn-coloured above, whitish beneath ; ears 

 long and hairy ; toes sparsely hairy ; tail nearly the length of 

 the body. 



Dimensions. — Length of the body three inches, of the tail, two 

 and a half inches. 



Habitat. — Southern States. 



Description. — Crowns of the molars similar in the arrangement 

 of the enamel to those of the type of the genus, as represented 

 by F. -Cuvier — " Dents des mammiferes ;" but the roots are 

 mostly cleft into four prongs : the inner surface of the inferior 

 incisors, grooved longitudinally ; ears very large, hairy within 

 and without ; legs small and weak, sparsely hairy ; fore feet 

 with four toes, armed with hooked nails; thumb rudimentary, 

 with a flat nail ; hind feet with five toes, armed with hooked 

 nails, all with sparse hairs extending to the roots of the nails ; 

 a callous tubercle at the inferior base of each finger, and two 

 others on the wrist ; tail long, cylindrical, and sparsely hairy ; 

 eyes large, black, and prominent. General colour of the 

 body above, plumbeous, each hair being tipped with brown- 

 ish yellow, presenting a fawn-coloured surface ; beneath 

 white. Whiskers composed of very long, fine, black and white 

 hairs. 



Like the musk-rat, (Ondatra, Lacep. or Fiber, Cuv.) this 

 quadruped differs from the arvicola principally in the possession 

 of roots to the molar teeth ; but for the existence of these roots, 



