734 THE EOCENE FAUNA. 



almost exactly like that of the Meniscoessus conquistus of the Laramie for- 

 mation, which is an ally, and perhaps belongs to the same family. The 

 arrangement described is an approach to what is seen in some of the The- 

 romorphous saurians of the Permian. The cotylus of the ulna has a 

 flared border adapted to the condyle of the roller. 



The astragalus has a concavity to represent the trochlear groove, and 

 the head is very small. It has a distal navicular facet, and an external 

 lateral facet for the cuboid. It is evident that digital reduction, cai'ried so 

 far in the Kangaroo, has made in this genus a considerable beginning. The 

 external two toes have been developed at the expense of the internal, which 

 were no doubt quite small, if not so much reduced as in Macropus. 



The new specimen of the C. pollux shows that the fourth premolar is 

 more distinct in its form from that of the genus Ptilodus than I had sus- 

 pected. Its crown consists of a single cusp, which is compressed at the 

 base and has a conic apex, which stands above the posterior root. The 

 large blade of the genus Ptilodus is represented by the anterior edge of this 

 cusp, and that of the anterior root with which it is continuous, at the ascent 

 of the ramus from the concave diastema. The genealogical table of Plagi- 

 aulacidce given on page 169 must then be altered. The genus Catopsalis 

 must stand out of the line connecting Ptilodus with Thylacoleo, on a branch 

 which terminates in the genus Polymastodon. This line will represent the 

 diminution of the fourth premolar to probable extinction. 



Catopsalis pollux Cope. 



American Naturalist, August, 1882 ; (July ), p. 685. 

 Plate XXIIIc; figs. 1-5. 



Parts of several individuals represent this marsupial, but there are no 

 examples of the maxillary dentition among them. The most complete 

 ramus supports the entire dentition. Associated with this are some entire 

 limb bones and vertebrae. 



The size of this species exceeded that of the Macropus giganteus, and still 

 more that of the Catopsalis foliatus. The ramus has the form of that of a 

 rodent, being vertically narrowed at the diastema, and deep at the molar 

 region. The inferior face widens and becomes flat posteriorly, and is more 



