sediments of the Moran Formation, near the base of the 
Permian system in north central Pexas. Phe seven stem 
fragments, averaging 4 cm. in length and 2.5 em. in 
diameter, are silicified, though with an admixture of cal- 
chum carbonate. 
The full diameter and exact shape of the stem) can 
only be inferred, owing to the more or less complete de- 
cortication which occurred prior to miuineralization. In 
one specimen portions of the inner cortex are retained, 
though in all specimens there has been partial removal 
of the woody tissue itself, presumably due to decay and 
abrasion before petrifiietion, 
Medullosa Olseniae.’ the deseription and diagnosis of 
which follows, is a medullosan stem of the “polystelic’~ 
type. Ttis, however, characterized by the absence of the 
so-called “'star rings” which feature many of the Euro- 
pean Permian members of Medudlosa described by Weber 
and Sterzel (1896) and subsequently figured by miuiuny au- 
thors. Our specimens indicate a stem, which, as deduced 
from the available material, developed a three- to five- 
membered vascular core, the components of which 
formed a system of anastomosing vascular bundles, each 
of which developed a concentric Cambium and corres- 
ponding secondary xvlem. Phe number of individual 
"The specific name is given in recognition of Kleanor L,. Olsen, wife 
of the Assistant Preparator of Vertebrate Paleontology of the Museum 
of Comparative Zoélogy, Harvard University, who collected the speci- 
mens in the field and made them available for study. 
*'The term stele in this discussion is restricted to the primary vas- 
cular system of the plant. Inasmuch as the primary vascular system 
im toto is designated stele, the use of the term  polystele is seem- 
inevly illogical. However, usawe has tended toward adoption of descrip- 
tive anatomical terms derived from living plants even though applied 
to fossil forms. Until a uniform system of terminology is developed 
for application to structures of both living and = fossil vascular plants, 
it seems necessary to follow the present conventions in descriptive 
terminology. 
12 
