378 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



narrow rim. A notch in the posterior margin divides this bounding ridge 

 into two portions, the hypoconid and hypoconulid-entoconid. The latter 

 cusps are not differentiated from each other. In worn teeth, the heel con- 

 sists of two rounded eminences, separated by a shallow groove. In con- 

 trast with the anterior molars, MT has a much smaller heel, ^enclosing a 

 small basin with a single prominent cusp on its posterior rim. An 

 antero-external cingulum is present on the second, third and fourth tooth 

 in the series. 



Milk Dentition. Ameghino states (1894, p. 109) that in Cladosictis 

 the canine, median and posterior premolars have deciduous predecessors. 

 The mandible represented in fig. 6, PL LIX, retains the deciduous tooth 

 replaced by the posterior premolar, the germ of which is visible beneath 

 the anterior root of the former tooth. Two large alveoli precede the de- 

 ciduous tooth, evidently for the roots of the median premolar. No tooth 

 germs were found beneath them. The region occupied by the anterior 

 premolar has been destroyed by fracture, and in repairing this break the 

 canine has been too closely approximated to the molars. The root of the 

 canine is hollow, indicating, not that it is a deciduous tooth, but that it 

 was not yet fully erupted and had not ceased its growth at the time of the 

 animal's death. The tooth replaced by the posterior premolar differs from 

 its permanent successor in the small size of the crown, which is greatly 

 compressed laterally, carrying a central cusp preceded by an accessory 

 basal cuspule. The narrow, ridge-like heel is subdivided by a shallow 

 notch into two cuspules. The first and second molars are fully erupted 

 and the third partly so. 



Skull (Plates LIV, fig. i; LV, fig. i; LVI; LXI, fig. i).-- Perhaps 

 the most striking peculiarity of this remarkable genus is the greatly elon- 

 gated, narrow skull, altogether disproportionate to the size of the body. 

 The facial portion is short and slender and the cranium elongated. The 

 post-orbital constriction is proportionately greater than in the much 

 smaller genus Amphiprovi'verra. The inclination of the upper border of 

 the facial profile varies with the species. The brain (PL LVI, fig. 3) was 

 less convoluted than in Thylacymis, and the brain case proportionately 

 much smaller. The ascending premaxillary processes have approximately 

 the same degree of development as in Amphiprovi'verm, and the nasals 

 are similarly expanded posteriorly. Well defined post-orbital processes 

 are present in C. lustrattts. A short distance above these processes, 



