144 THE PALEONTOLOGY OF MINNESOTA. 
[Phyllodictya,. 
differences are to be found inthe character of the interspaces, and in the shape of 
the zoarium. 
Formation and locality—Rare in the Trenton shales, at Minneapolis, Minnesota. The types of the 
species are from the Birdseye limestone at High Bridge, Kentucky. 
PHYLLODICTYA VARIA, ”. Sp. 
PLATE XIV, FIGS. 1-8. 
Comp. Stictopora labyrinthica HALL, 1847. Pal. N. Y., vol. i, p. 50. 
Zoarium variable, consisting of broad, leaf-like, thin expansions, either simple 
or with irregular marginal incisions, or of wide branching fronds, with the edges 
subparallel, sharp, and non-poriferous. At intervals of about 4 mm. the surface 
exhibits subsolid, even or slightly depressed spots or “macul,” smooth when worn, 
finely grano-striate as well as faintly channeled longitudinally when well preserved. 
In the youngest examples these macule are small and sometimes scarcely distinguish- 
able, but with age they seem to increase in size (compare figs. 2 and 7). The most 
obvious and normal arrangement of the zocecial apertures is in longitudinal series, 
twelve or thirteen in 5 mm., between delicate papillose ridges; but the general 
aspect of the surface varies greatly in the specimens before me. Some of these dif- 
ferences are doubtlessly due to, or exaggerated, by weathering and other accidental 
causes, yet others are as clearly changes consequent upon increasing age, and thus 
are to be regarded as expressing different stages in the development of the zoarium. 
In the youngest the zocecial apertures are very oblique, with a rim, strongly elevated 
at the posterior side, and dying out at the sides or seeming to unite with the delicate 
ridges separating the rows. This condition is represented in figs. 2 and 3. In later 
stages the longitudinal ridges becomes indistinct, the interspaces flatter, the poster- 
ior “lip” less pronounced, the apertures less oblique and, sometimes, a little smaller, 
while in other cases, probably representing a weathered condition, they appear 
larger, with the interspaces rounded. The longitudinal arrangement also becomes 
less obvious but never, so far as observed, quite subordinate to the diagonal. This 
may seem to have occurred over limited spots, especially when the macule are unusu- 
ally large as in the specimen represented by figs. 6 and 7. 
Only one specimen proved suitable for sectioning. This even failed to preserve 
the minuter details of structure as well as was desired. So far as the internal char- 
acters could be made out they are shown in figs. 4 and 5, excepting that by an unac- 
countable oversight the diaphragms were not drawn in the vertical sections. Each 
tube should have shown one diaphragm crossing it at right angles at a point about 
midway between its aperture and the mesial line. 
