SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 
415 
Length, My-My on alveolar border 
Antero-posterior diameters of My, My and My each . 
Transverse “ “ and My each 
“ “ “ My 
Depth of mandible below anterior premolar 
“ “ “ “ M t 
“ “ “M T 
Antero-posterior diameters of M^- and M^- each 
Transverse “ “ M- 2 . .... 
” “ “ M— 
Antero-posterior diameter of auditory bulla 
Transverse “ “ “ “ . . 
Width of humerus at distal end “ “ . . 
Greatest width of radius proximally .... 
Diameter of radial shaft ...... 
Greatest width of ulna at lower margin of sigmoid cavity 
.007 
.002 
.0015 
.001 
.0035 
.0044 
.0048 
.002 
.0022 
.002 
.01 1 
.0048 
.0075 
.0023 
.0013 
.004 
Microbiotherium patagonicum Ameghino. 
(Plate LXII, Figs. 5, 5 a.) 
Microbiotherium patagonicum Amegh. ; Enum. Sist. Especies Mamif. Fos. 
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 My inclusive . . . .007 
Length of space occupied by the premolars ...... .003 
“ “ “ “ “ “ first and second molars .... .0028 
Antero-posterior diameter of My ........ .0016 
Transverse “ “ “ ........ .001 
Antero-posterior “ “ My ........ .0015 
Transverse “ “ “ ........ .001 
Depth of mandible below posterior premolar ...... .002 
