1881.] . Geology and Paleontology. g21 
(From the American Naturalist, November, 1881.) 
GEOLOGY AND PALAONTOLOGY. 
Eocene PLaGiAuLaciD®.—This remarkable family of Marsu- 
piaha belongs, as is well known, to the Jurassic period, and genera 
have been found in both Europe and North America. Falconer 
traced resemblances to the existing Hypsiprymnus of Australia, 
and there might be some remote affinity between the families. 
But in the formations which represent the long period between 
the Jurassic and present ages, no trace of intervehing genera has 
been found. It is therefore of interest that I am able to announce 
the discovery of such a one from the Lowest Eocene (perhaps 
Puerco) beds of New Mexico. The specimen was found with the 
jaw of the Zriisodon quivirensis (NATURALIST, for August, 1881), 
and consists of a single tooth of the lower jaw. It is the charac- 
teristic obliquely ridged cutting tooth well known in Plagiaulax. 
It presents the following differences from those of Plagzaulax and 
Ctenacodon, which I regard for the present as generic. 
Char. gen. Cutting edge convex and continuous with. the an- 
terior edge of the crown, and serrate from the union of ridges 
which ascend on each side. Ridges curved backwards, all reach- 
ing the edge excepting above the posterior root of the tooth, 
where they are discontinued, leaving a smooth edge. In Plagiau- 
/ax the ridges are continued to the posterior edge of the crown, 
and in Ctenacodon the ridges do not extend on the sides of the 
crown, In Aypsiprvmnis the ridges are vertical. 
Char. specif. The tooth is much larger than that of any of the 
