SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 427 



4 and 5). The lower molars are lophodont, the cusps of the trigonid and 

 heel forming crescentic ridges. All the molars are double-rooted and de- 

 crease rapidly in size posteriorly. 



The first is modified as a sectorial by the elongation of the protoconid- 

 paraconid blade. Vertical ridges are not developed on the sectorial, but 

 the enamel on the outer side is irregularly crenulated. The paraconid is 

 lower than the protoconid, from which it is separated by a distinct notch. 

 In this respect, Palceothentes is intermediate between the Caenolestinae and 

 the "more specialized Palaeothentinae, Callomenus and Decastis. The 

 second and third molars are similar in pattern to the first, but the para- 

 conid is reduced and the horn of the posterior crescent, instead of uniting 

 with the metaconid, as in the sectorial molar, is shifted farther toward the 

 outer side, uniting with the anterior crescent between the protoconid and 

 metaconid, as in Callomenus and Decastis (cf. PI. LXIII, fig. 6a ; PI. 

 LXIV, figs. 5, 6a). The fourth molar is a small tooth similar to those 

 preceding it, but losing early by wear the details of the crown pattern. 

 External cingula are faintly indicated on the anterior lobes of the first and 

 second molars. 



Skull '(PI. LXIII, fig. 3; PI. LXIV, figs, i, i*). A skull of P. inter- 

 medius in the Princeton collection (No. 15,225), lacking the region anterior 

 to the canine and posterior to the glenoid fossae, forms the basis for the 

 following description. In side view (PI. LXIII, fig. 3), the skull is seen 

 to be gently arched, the highest point lying at the junction of the temporal 

 ridges. Back of the orbits, the brain case contracts, becoming widely 

 expanded posteriorly. Postorbital frontal processes are wanting, but well 

 marked temporal ridges give rise to a low sagittal crest. Between the 

 orbits, the frontal is plane. Anteriorly, it sends a broad bar forward 

 between the nasal and lachrymal to join the maxillary, differing in this 

 respect from the Santa Cruz marsupial carnivores. 



The nasals are very broad behind, rapidly decreasing in width anteriorly. 

 Unlike Ccenolestes, there is no trace of an antorbital vacuity. The pre- 

 maxillae have been largely broken away, but resemble those of Gzno/estes 

 in sending a narrow tongue between the maxillary and nasal (cf. PI. 

 LXIII, fig. 14; PI. LXIV, fig. ia). The lachrymal has but little facial 

 extension. The lachrymal duct opens within the orbital rim, which sup- 

 ports a small but distinct lachrymal tubercle. 



The anterior margin of the orbit is sharply defined. The jugal arches 



