446 PROCEEDINGS OF THE ACADEMY OF 



The astragalus, which I have seen in several of the species, pre- 

 sents a corresponding trochlear face. That is, instead of a groove, 

 it presents an open angle upwards, which separates the superior 

 from the oblique internal face. The superior plane is flat, but is 

 interrupted on the posterior side by a groove. This groove is the 

 posterior extremity of that which divides the superior face of the 

 astragalus in the higher Mammalia, but here it contracts to a 

 point and disappears next the fibular face just as it reaches the 

 superior surface. The fibular face is vertical, and shares on its 

 posterior part a large ligamentous fossa with the opposed part of 

 the fibula. The distal end of the fibula is remarkably stout. 



This structure finds its counterpart in the internal half of the 

 astragalus of the opossum. The arrangement permits a rotary 

 movement of the astragalus and thus of the whole foot, on the 

 tibia, the fibula, with its fixed articulation with the astragalus, 

 rotating on the tibia, as in thepedimanous Marsupialia. The flat- 

 ness of the inner malleolus in some of the species indicates that 

 the capacity for rotation was less in them than in others. This 

 arrangement exactly reverses the extensive oblique fibulo-astraga- 

 lar articulation seen in the opossum, the Petaxirista, Dasyurus,etc. 

 Prof Owen, in describing the astralagus of the wombat (Phasco- 

 lomys), says : " The upper articular surface for the tibia is as usual 

 concavo-convex, the internal surface for the inner malleolus flat- 

 tened, and at right angles with the preceding, but the outer articu- 

 lar surface presents a triangular flattened form, and, instead of 

 being bent down parallel with the inner articular surface, slopes 

 away at a very open angle from the upper surface, receiving the 

 articular surface of the fibula so as to sustain its vertical pressure. 

 * * * This form of astragalus is also characteristic of the 

 Koala, Petaurists, Dasyures, and the Pedimanous Marsupialia." 

 In one species where the cuboid bones are preserved, it is evi- 

 dent that the distal end of the astragalus articulated with this as 

 well as with the navicular bone, although the facet of the astraga- 

 lus is single and continuous. As the extensive transverse distal 

 astragalar face is characteristic of all the species where it is pre- 

 served, the contact of the cuboid and astragalus is probably com- 

 mon to all of this division. 



The dentition of this group is consistent with its reference to 

 the sarcophagous Marsupialia or to the Insectivora. It has, how- 

 ever, decided resemblances in the form of the molars, and in the 

 deficiency in the number of the inferior incisors, to such genera 

 of Insectivora as Mythomys and Solenodon, while in the large 

 canines, it more nearly approaches Sarcophaga and Carnivora. 



I propose to include the genera Ambloctonus, Oxysena, Stypolo- 

 phuSj and Didymictis in a special division under the name of 

 Greodonta. This division may be regarded as a suborder of the 

 Insectivora. It is possible that the genus Diacodon Cope belongs 

 here also ; its species resemble Chiroptera in the inferior dentition, 



