226 THE PALEONTOLOGY OF MINNESOTA. 
{Atactoporella ramosa. 
is shown in figures 18 to 20 (pl. XV), consist of a gradual thickening of the zocecial 
walls, and strengthening of the acanthopores, causing the mesopores, which in the 
thin-walled regions are large and distinct enough, though never as numerous as in 
most other species of the genus, to be more or less completely obliterated. Cysti- 
phragms occur in every zoccial tube. The opening in them varies from subcircular to 
semiovate, according as they are situated subcentrally or at one side of the zowecium. 
Vertical sections (pl. XV, fig. 21) show that the cystiphragms and diaphragms in both 
sets of tubes are equally crowded. It is, therefore, difficult to distinguish the meso- 
pores from those zocecial tubes in which the curved section of the cystiphragms is 
not shown. 
This is a well marked species and readily separated from A. schucherti Ulrich, 
and certain varieties of A. insweta, which it resembles chiefly in the large size of the 
acanthopores, by the much greater abundance of transverse partitions in the tubes. 
The zoarium is also heavier, and the zocecial walls thicker. A nearer relative 
apparently than either of the species compared is found in an undescribed species 
occurring near the tops of the hills at Cincinnati, Ohio. 
Among associated species that might be confounded there are two of Leptotrypa, 
one, a parasitic undescribed form, the other, subglobular, described in this volume 
as L. acervulosa. Both are distinguished externally by having much thinner walls 
and inconspicuous acanthopores. When sectioned the Leptotrypas will of course be 
separated at once by the total absence of cystiphragms. 
Formation and locality.—Galena shales, St. Paul and near Cannon Falls, Minnesota. 
ATACTOPORELLA RAMOSA, ”. Sp. 
PLATE XX, FIGS. 22-27. 
Zoarium erect, subramose, branches compressed, dividing once or twice, 3 to 6 
mm. thick, 5 to 10 mm. wide. Surface minutely spinulose, and elevated at intervals 
of about 2 mm. into small monticules, varying in different examples from low and 
rounded to prominently conical in shape. Slopes of monticules occupied by cells of 
slightly larger size than the average; their summits, however, often appear solid, 
these being, in most cases, formed by small aggregations of closed mesopores. 
Zocecial apertures small, floriform, about sixteen in 3 mm., separated by interspaces, 
in which but few mesopores can be detected, of less width than their diameter ; 
each surrounded by from five to seven small acanthopores, projecting well into the 
zocecial cavity. This describes the fully matured and ordinary appearance of well 
preserved specimens. Young stages are quite different, the zocecial apertures being 
