Sinclair: typotheria of the santa cruz beds. 107 
ridge as in /. rodens , but less accentuated in the molars and with the 
second depression broader, already well-marked in P- and P-. All the 
upper teeth except P- have the anterior part considerably broader than 
the posterior. P- measures .0045 X .002. P- and P A are .004 long on 
the outer side but only .0025 on the inner ; maximum breadth .0035. 
The true molars are somewhat broader on the inner side and diminish 
slightly in size from M- to M-. Length, P 1 to M- .028 following the 
curve of the series and only .026 in a straight line. A small fragment 
of the anterior part of the skull with the premaxilla shows that behind 
the first incisor, in the palate, were two large incisive foramina as in 
Pachyrukhos, instead of the incisive notch of Typotherium. The lower 
dentition presents nothing peculiar except for the slightly larger size, but 
the teeth are in a more continuous series, the short diastema between the 
canine and P T having disappeared. Length P T to .027 ; depth of jaw 
at M t .015. The symphysis measured on the outer side is .014 long. 
There are three mental foramina, the anterior and largest below the 
canine, the second and smallest below P2 and the third beneath P T . I 
have of this species the two rami somewhat broken with three molars of 
the first dentition still but little worn and the first true molar. The de- 
ciduous molars, bilobate by two opposite grooves, have separate roots. 
These teeth, deciduous molars and true molars, have the peculiarity of a 
small notch or cavity on the inner side of each lobe, very superficial and 
soon disappearing on wear, but which evidently correspond to the two 
inner folds of Toxodon , Protoxodon , Colpodon, etc., as also of many pachy- 
derms, such as Homalodontotherium , Macrauchenia , etc. (’89, 468-469). 
PACHYRUKHOS. 
Pachyrukhos teres Ameghino. 
Pachyrucos teres Amegh.; Contrib. al Conoc., etc., p. 429, PI. 13, figs. 
25-27, 1889; Enum. Synoptique, etc., p. 19, 1894 (listed); Segundo 
Censo, etc., p. 15 1, 1898 (listed). 
One half smaller than P. typicus * but is very similar in general con- 
formation. P- is not so disproportionately smaller than P- as in the 
latter, but is only slightly so. Its anterior part is also less compressed 
than in the other species and is of perfectly elliptical section. P-, is 
slightly larger, is of the same shape as P- and both are inserted obliquely. 
* A Monte Hermoso species. 
