418 OLDER MESOZOIC FLORAS OF UNITED STATES. 
Dr. Knowlton finds the wood probably to belong to the genus Arau- 
carioxylon, but to be specifically distinct from any hitherto described. 
His note upon it is as follows: 
DESCRIPTION OF A NEW SPECIES OF ARAUCARIOXYLON FROM THE CYCAD BED OF THE FREEZEOUT 
HILLS, CARBON COUNTY, WYOMING. 
By F. H. KNow ton. 
ARAUCARIOXYLON? OBSCURUM Knowlton n. sp. 
Pl. CLXXVIII. 
Annual ring not apparent to the naked eye, the line of demarcation 
between the rings consisting of only four or five slightly modified 
layers of cells; wood cells very small, approximately square in cross- 
section, thick walled, provided on the radial walls with a single row of 
small contiguous or weathered bordered pits; medullary rays in a single 
series of 1 to 8 superimposed cells; resin cells and resin passages wholly 
wanting. 
Transverse section: The appearance of the wood in this section is well 
shown in the figure (Pl. CLX XVIII, Fig. 1). The wood cells are seen 
to be of very uniform size and shape and are quite thick walled. The 
growth rings can not be made out by the naked eye, but under the 
microscope they are found to be quite broad (2 to 3 mm.) and to be sepa- 
rated by only four or five layers of slightly thicker cells. The absence 
of longitudinal resin cells or passages is also well shown in this section. 
The medullary rays appear as long remotely broken cells. 
Radial section: The wood cells as seen in this section are provided 
with a single row of small bordered pits. Usually they are somewhat 
remote, as shown in Figs. 1 and 2 of Pl. CLX XVIII, but occasionally 
they are contiguous and slightly modified in shape by contact with each 
other. Theinner pit is often minute, but the preservation is not good 
enough to permit measurements. The medullary rays are seen to be 
made up of relatively long slender-walled cells and probably without 
markings, although there is some evidence to show that there may have 
been narrow slits or oblong pores in their cell walls. This evidence, 
however, is not conclusive. 
Tangential section: The wood cells are without pits or markings on 
this wall, at least so far as can be made out. The medullary rays 
are very numerous and composed of from one to not more than twelve 
superimposed cells, and usually the number is from three to perhaps 
five or six. They are very small and have relatively thick walls. 
Discussion: The placing of this wood in the genus Araucarioxylon 
is open to more or less question, yet as it approaches more closely to 
this genus, I have tentatively so referred it. It has the obscure growth 
rings usually to be observed in this genus, but is without certain other 
characters. The medullary rays are similar to those of numerous species 
of Araucarioxylon, but the pits with radial walls of the wood cells are 
