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 : Canolestes, Halmarhiphus, Garzonia. 



Second Subfamily: PALAEOTHENTINAE. Dental formula ,, \. 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 (Palaothentes). Lower molars lophodont. M T with prominent metaconid. Pos- 

 terior lower premolar double-rooted and functional or single-rooted and reduced. 

 Genera : Palceolhentes, Callomenus, Decastis. 



Third Subfamily : ABDERITIN^E. 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 M-J-. 

 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 Caenolestinae (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, PL 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 Palaeothentinae 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 Palaeothentinae (Callomenus and Decastis] from a tooth of the Hal- 

 marhiphtts type is plainly indicated by the intermediate condition in 

 Palaothentes. 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 



