610 The American Naturalist. [July, 
but should apparently be placed with Stereognathus (with which 
its resemblance in molar structure has always been recognized) in 
a distinct family, the Stereognathidz, distinguished by the pres- 
ence of two rows of tubercles in the upper molars and three in 
the lower, of the crescentoid pattern. The more numerous 
tubercles in Meniscoéssus would accord well with its more recent 
character. 
There are thus apparently only two families of the Multituber- 
culates represented here,—unless, as the author has suggested, 
Allacodon belongs to the Bolodontide. We have yet to find the 
successors of the Tritylodontide and predecessors of Polymas- 
todon and Chirox of the Lower Eocene.” 
As for the Trituberculate forms, there are evidently two distinct 
genera, which probably belong to different families. The types of 
Didelphops and Cimolestes closely resemble molars found respec- 
tively among the Mesodonta, the Creodonta, Insectivora, and 
Marsupialia. Their systematic position is, therefore, very uncer- 
tain from this evidence. They mark, however, a very great 
advance upon the Jurassic forms in tooth evolution. We find in 
Didelphops the earliest low-crowned tritubercular molar which has 
_ been obtained, with one or two intermediate tubercles; while the 
lower molar is the earliest quinquetubercular tooth known. The 
Cimolestes molar is tuberculossectorial, and presents a marked 
advance upon Jurassic tooth types, but has, nevertheless, a broad 
talon, with both the entoconid and hypoconid developed, whereas 
all Jurassic forms present the hypoconid only. 
The bones of the appendicular skeleton present a number of 
very interesting points, some of which the author mentions. 
These are: the coracoid facet upon the scapula ; the interclavicular. 
We note also the flat astragalus, without a neck, apparently per- 
forated by an astragalar foramen, and with a broad cuboidal 
facet as well the navicular facet. The calcaneum has a narrow 
sustentaculum, 
1 The nearest resemblance to Polymastodon is that observed in the striated lower 
= rS in Figure 5. This genus will undoubtedly be found represented 
18 This observation rests solely upon the figure. All astragali of the Lower Eocene 
display this foramen. 






