Sinclair: marsupialia of the santa cruz beds. 437 
The last vestigial tooth (PI. LXIV, fig. 6), probably representing the 
median premolar, has a cylindrical, blunt-pointed crown. The crown of 
the third intermediate (PI. LXIV, fig. 4), overhangs anteriorly. The first 
two rudimentary teeth have been shed, but from the obliquity of their 
alveoli, it is probable that they resemble the homologous teeth in Palceo- 
thentes. 
The molars are an exact duplication of those of Callomenus , but are 
slightly more worn in both the mandibles in the collection. The last 
tooth is double-rooted, but has, unfortunately, been broken off. 
The number and relative position of the mental foramina is much the 
same as in Callomenus. The apparent shifting forward of the anterior 
foramen is due to the reduction in length of the premolar series. The 
masseteric fossa is imperforate and the coronoid broad and high with 
prominent anterior margin. The symphysial impression is wider than in 
Callomenus. 
Difference in size is the only character available for the separation of 
the two species recognized by Ameghino (1891, p. 305), of which the 
larger, D. columnaris , is represented in the collection by two specimens. 
Decastis columnaris Ameghino. 
(Plate LXIV, Figs. 4, 4 a, 6, 6a.) 
Decastis columnaris Amegh.; Nuevos Restos Mamif. Fos. Patagonia Aus- 
tral, p. 19, Aug., 1891 ; Revista Argentina, I, entr. 5 a, p. 305, Oct., 
1891. 
Like Callomenus ligatus , Decastis columnaris is known only from lower 
jaws, of which parts of two are in the collections at Princeton University 
and the American Museum. No. 15,710, collected by Mr. Peterson at 
Coy Inlet, is a portion of the left half of a mandible, with two premolars 
and three molars in place (PI. LXIV, figs. 6, 6a). The second specimen 
(No. 9594 American Museum) from the Santa Cruz beds, on the Rio 
Gallegos, is the anterior half of a right mandibular ramus retaining' in 
place two molars, the third vestigial tooth and the base of the incisor 
(PI. LXIV, figs. 4, 4 a). 
Measurements. 
No. 13,710. No. 9594. 
Approximate length, posterior border of median incisor to M T 
inclusive 
Length of space occupied by vestigial teeth and posterior premolar. >0055 
