Sinclair: marsupialia of the santa cruz beds. 417 
tubercular ( Ccenolestes ). Lower molars tuberculo-sectorial, approaching lophodont when 
worn. Median and posterior lower premolars double-rooted and functional. 
Genera : Ccenolestes , Halmarhiphus , Garzonia. 
Second Subfamily: PALAiOTHENTINAd. — Dental formula AA, t. Posterior superior 
premolar and first lower molar sectorial in function. Sectorials unstriated. First upper 
molar fully quadritubercular, second with rudimentary hypocone, third and fourth tritu- 
bercular ( Palceothentes ). Lower molars lophodont. My with prominent metaconid. Pos- 
terior lower premolar double-rooted and functional or single-rooted and reduced. 
Genera : Palceothentes , Callomenus, Decastis. 
Third Subfamily : ABDERIT1NAI. — Dental formula First lower molar with proto- 
conoid-paraconoid blade developed into a striated sectorial shear with serrate margin, 
greatly elevated above the general level of the tooth row. Metaconoid absent on My. 
Second, third and fourth lower molars buno-lophodont. Functional lower premolars 
wanting in known Santa Cruz forms, the posterior tooth being single-rooted and vestigial. 
Genus : Abderites. 
As many of the genera are known only from the lower jaw, it has 
seemed advisable to insert parenthetically in the preceding descriptions 
the names of those forms on which important observations regarding the 
upper dentition and feet are based. In writing the dental formulas, the 
number of lower vestigial antemolars of questionable homology is indi- 
cated in italics, while figures in roman type express the number of teeth 
which can be definitely homologized. 
In the Caenolestinse (PL LXIII, figs. 8, 9, 14) the full complement of 
lower premolars is retained. The antemolar formula in Halmarhiphus 
and occasionally in Ccenolestes (Bensley, 1903, p. 124, PI. 5, fig. 38) is the 
same as in Didelphys. In a specimen of Garzonia in the collection the 
antemolar formula is nine, but this may be tentatively regarded as an 
individual peculiarity, since the constancy of its occurrence has not been 
confirmed. In the case of the Palaeothentinse and Abderitinae, it cannot 
be determined at present whether the reduction in the number of vestigial 
teeth is to be accounted for by the loss of incisors, canine or pre- 
molars. 
The elaboration of the sectorial lower molar in the larger members of 
the Palaeothentinse ( Callomenus and Decastis ) from a tooth of the Hal- 
marhiphus type is plainly indicated by the intermediate condition in 
Palceothentes . In this genus the anterior lobe of Mr is proportionately 
longer and higher than in Halmarhiphus or Ccenolestes , but the paraconid 
is decidedly lower than the protoconid, from which it is separated by a 
distinct notch, as in the latter genus. In Callomenus and Decastis the 
