SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 415 



Length, M T -M T on alveolar border 007 



Antero-posterior diameters of M T , M^ and Mj each 002 



Transverse " " M f and Mj each ooi 5 



" M, . .001 



Depth of mandible below anterior premolar ...... .0035 



. " " " M T 0044 



" " " M T 0048 



Antero-posterior diameters of M^ and M* each 002 



Transverse " "Ml OO22 



" Mi 002 



Antero-posterior diameter of auditory bulla oil 



Transverse " " " " ...... .0048 



Width of humerus at distal end " " . . . . . . .0075 



Greatest width of radius proximally ........ .0023 



Diameter of radial shaft .......... .0013 



Greatest width of ulna at lower margin of sigmoid cavity .... .004 



MlCROBIOTHERIUM PATAGONICUM AmeghinO. 

 (Plate LXII, Figs. 5, 5*.) 



Microbiotherium patagonicum Amegh. ; Enum. Sist. Especies Mamif. F6s. 



Patagonia Austral, p. 6, 1887. 



A minute species, represented by the anterior portion of a right man- 

 dibular ramus, with the posterior premolar-and two molars in place, col- 

 lected by Mr. Barnum Brown on the Rio Gallegos (No. 9121 American 

 Museum of Natural History). The remaining premolars, the canine and 

 the incisors are represented by alveoles. 



,The premolars are closely crowded and the anterior tooth is placed 

 obliquely to the axis of the jaw. There is no external cingulum on the 

 molars. The remaining dental characters, so far as determinable, are of 

 generic importance and have already been noticed. The species may be 

 recognized by its small size. 



MEASUREMENTS. 



Length from anterior portion of canine alveolus to Mj inclusive . .007 



Length of space occupied by the premolars .... . .003 



" " " " " " first and second molars 0028 



Antero-posterior diameter of M-j- ..... .0016 



Transverse " " ... .001 



Antero-posterior " " Mj . .0015 



Transverse " " " -OOi 



Depth of mandible below posterior premolar . . .002 



