MARTIN: A COMPARISON OF THREE SKULLS. 391 
depth of from thirty to forty feet, and in many places the 
Bethany Falls limestone is exposed in considerable areas at 
the bottom of the river. About two and a half miles below 
where the specimen was exhumed, and just below the bridge 
that crosses the Marais des Cygnes at Trading Post, a small 
deposit of bones was found several years ago by Mr. Amos 
Tubbs, of Trading Post. This small collection the writer ex- 
amined a year ago, and recognized in it teeth of elephant, 
horse, camel, together with limb bones and a tusk of an ele- 
phant, all belonging clearly to the Pleistocene. At the point 
where the bones were found, the river has cut clear down to the 
Bethany Falls limestone. Directly above the limestone occurs 
a layer of conglomerate about eighteen inches thick, above this 
a like thickness of bluish-gray silty deposit in which the bones 
were found. The depth at which these were discovered and 
the material in which they appeared tallies well with the data 
at hand concerning the Castoroides skull, so that it will not 
be unreasonable to suppose that at one time the layer in which 
the skull was found was once the old river bed, or the bottom 
of some body of water adjacent to the river. The fact that the 
bones found at Trading Post were in the same deposit and at 
about the same depth clearly indicates that Castoroides was 
contemporary with these forms. 
To those unacquainted with the geology in the vicinity of 
Trading Post it may be well briefly to enumerate the layers as 
they occur where Mr. Tubbs’ bone bed was exposed: 
From the general level of the valley: 
Six feet of black loam. 
Twelve feet marly clay. 
Twelve feet blue and yellow marl, verging into shale. 
Eighteen inches of bluish silt in which the bones were found. 
Eighteen inches conglomerate lying on the heavy Bethany Falls 
limestone. 
The conglomerate beds and the blue silty material occur only 
in isolated patches of a few feet in length; that in which the 
bones were found was probably twenty-five feet in length. 
THE SKULL. 
The typically rodent-like skull more closely resembles that 
of Castor fiber than of any other of the rodent family, yet in 
many respects close analogies are found to that of the Biza- 
cacha (Lagostomus trichodactulus), a living form found on 
