178 THE PALEONTOLOGY OF MINNESOTA. 
{Anthropora. 
In figures 21 a, b, c, | have endeavored to show all the characters of the zocecia 
that are to be brought out in tangential sections. The right sides of a and 6 repre- 
sent the structure just beneath the surface, while the left sides show it at a deeper 
level in the section. In 21 ¢ only the primitive or prostrate portion of the zocecia is 
shown. 
The unbranched character of the segments of this species, as well as their greater 
length, will distinguish them at once from all other species of the genus. 
Formation and locality—Very abundant in the lower and middle thirds of the Trenton shales, at 
Minneapolis, St. Paul, Fountain and other localities in Minnesota; Decorah, Iowa. 
Mus. Reg. Nos. 5933, 8075. 
ANTHROPORA BIFURCATA 2. Sp. 
PLATE XIV, FIGS. 22-25. ~ 
Segments small, thin, with sharp edges and rather wide non-poriferous border, 
the lower ones bifurcating, usually only once; so far as observed not over 8 mm. 
long, and from 1.2 to 1.8 mm. wide; the upper joints shorter, their length occa- 
sionally less than 5 mm., bifurcating, or with a single lobe-like projection on one or 
both sides. Young segments with comparatively large, ovate zoccial apertures, not 
very regularly arranged in longitudinal and diagonally intersecting series, with 
about nine in 3 mm. lengthwise, and five in 1 mm. diagonally. Apertures enclosed 
in distinct granulose rims, connecting longitudinally. Interspaces depressed, some- 
times with a few indistinct strie. With age the zocecial apertures become more 
circular and smaller, and the peristomes and connecting ridges thicker. 
This species is related to A. shafferi (Meek) but differs in having only one ridge 
or line in the interspaces, instead of from one to four. A. simplex has longer and 
unbranched segments, while A. veversa has a peculiar horseshoe-shaped ridge about 
its zocecial apertures. 
Formation and locality.—Detached segments rather common in the Galena shales and in the upper 
third of the Trenton shales at St. Paul, and Cannon Falls, Minnesota. A closely allied species, perhaps it 
is identical, in the Trenton limestone of Kentucky, Tennessee, and Canada. 
Mus. Rey. No. 8108. 
ARTHROPORA REVERSA 1. Sp. 
PLATE XIV, FIG. 26. 
Of this species I have seen only two segments, but their superficial aspect is so 
distinctive that I do not hesitate in proposing a new name for them. One of these 
is 8 mm. long, and divides dichotomously about midway the length. ‘The two forks 
are of the same strength as the lower half, averaging 1.2 mm. wide, the three 
extremities abrupt and tipped for articulation with the preceding and succeeding 
