INSECTIVORA OF THE SANTA CRUZ BEDS. 379 



of the tarsus as is preserved displays but little resemblance to that of 

 Chrysochloris. 



Among the loose bones associated with one of the specimens is one 

 which much resembles the falciform bone which is attached to the tarsus 

 in Notoryctes, but its reference is quite uncertain. 



Relationships. The taxonomic position of Necrolestes would seem to be 

 reasonably clear. It cannot well have had any direct connection with 

 Notoryctes, because the latter is in every essential respect a marsupial, 

 while Necrolestes is as distinctively one of the Insectivora. The presence of 

 four upper incisors is no indication of marsupial affinities, since even in 

 the modern Soricidce there are four incisors in the premaxillary. Though 

 there are many resemblances between the South American and the Aus- 

 tralian genus, it can hardly be doubted that these resemblances are due 

 to convergence, as are also the many likenesses between Chrysochloris 

 and Notoryctes. On the other hand, the similarites of Necrolestes to Chry- 

 sochloris seem probably to be due to genetic relationship. This conclusion 

 is justified not only because the resemblances between the two genera are 

 so numerous and so close, but also because even the differences are, for 

 the most part, such as usually occur between the earlier and later members 

 of a phylum or of two allied phyla. 



The resemblances are to be found in all parts of the structure. The 

 dentition is of very similar type in the two genera, especially the molars and 

 the posterior premolars. The incisors and canines of Chrysochloris are 

 modernized in a way that, as Leche has shown, has been frequently re- 

 peated within the limits of the modern insectivorous families. Aside, 

 perhaps, from the relatively large size of the canines, the dentition of 

 Necrolestes is one from which that of Chrysochloris might readily have 

 been derived. The same is true of the skull ; in most respects the skull 

 of the African genus is much the more differentiated of the two. This is 

 especially to be seen in the inflated condition of the temporal region in 

 Chrysochloris, but the skull of Necrolestes is not far removed from what 

 the ancestral type of the former probably was. 



The vertebrae of Necrolestes in all regions of the column are remarkably 

 like those of Chrysochloris (except that the former had a much better de- 

 veloped tail) differing from them in only a few details, while those of both 

 genera are altogether unlike the characteristic vertebrae of Notoryctes. 



Imperfect specimens of the scapula resemble Notoryctes rather than 



