I go I.] Matthew, Additional Observations on the Creodo?ita. 35 



in the centra, and heavy in the arches — apparently short-spined. 

 The calcaneum has a small fibular facet. The astragalus is very 

 short and wide, with flatter trochlea, shorter neck, and smaller 

 sustentacular process than in F. ossifraga; it has the distinct 

 cuboidal facet common to the Mesonychidae, and the navicular 

 facet is flat transversely (slightly concave in P. ossifraga, flat in 

 Dissacus, convex in M. obtusidens).^ 



The most interesting point in regard to this animal is the 

 question of the succession of the teeth. If, as our specimens 

 seem to indicate, the fourth premolar belongs to 

 the milk series, and is not replaced by a permanent 

 tooth, then this species approximates the marsupial 

 dental formula, with four true molars and three 

 premolars. The progressive inflection of the angle 

 of the jaw in the Mesonychid phylum is another 

 character of some importance approximating them 

 to the Marsupials. From what we know of the 

 phylum we must regard both these characters as 

 acquired in the Mesonychidae ; the question then 

 arises — are they not also acquired in the Marsupi- 

 alia ? This is a matter hardly suitable for discus- 

 sion within the limits of this paper ; I present the 

 evidence for what it is worth. That there is a pro- 

 gressive inflection of the lower jaw in the Meson- 

 ychidae is certain; the evidence for the retention of 

 the fourth milk molar may be summarized as fol- 

 lows : 



1. In the upper jaw the last premolar has the ordinary charac- 

 ter of a milk molar (small size, short roots, thin enamel, precocious 

 molarization) and is more worn than the first molar or the third 

 premolar, hence probably appeared before either of them. 



2. In the lower jaw the fourth premolar has disappeared and 

 its alveolus closed up in an adult specimen, while in a young in- 

 dividual indications exist of an early protruded tooth, but none 

 of a replacing tooth although the third permanent premolar is 

 completely formed and emerging from the jaw. 



This evidence cannot be considered satisfactory, especially in 



Fig. 17. Pacli- 

 yana gigantea. 

 No. 2959. Left 

 calcaneum and 

 astragalus, from 

 above, one- 

 fourth natural 

 size. 



' Professor Scott's statement regarding the last species is that the navicular is concave in 

 both directions. This involves apparently an astragalus convex both ways. 



