204 THE PALEONTOLOGY OF MINNESOTA, 
[Nematopora. 
vails. The surface is striated, especially on the more regularly constructed segments, 
very much as in A. pulchellum. Though inclined to regard it as an illy nourished 
variety of that species, with shorter and more slender segments, I prefer, for the 
present, to leave the form unclassified specifically. 
All the specimens of this form were collected by me in the upper part of the 
Trenton shales at St. Paul, Minnesota. 
Genus NEMATOPORA, Ulrich. 
Nematopora, ULRICH, 1888, The American Geologist, vol. i, p. 284; 1890, Illinois Geol. Surv., vol. viii, 
pp. 401 and 644. 
Zoaria very slender, branching, continuous above the pointed basal extremity. 
Zocecia subtubular, short, arranged in a radial manner around one or two exceed- 
ingly minute axial tubes. Apertures arranged in longitudinal series between smooth 
or granulose ridges, nearly direct, generally elongate-ovate and enclosed by a thin 
peristome. One or two diaphragms occasionally present. 
Type: N. ovalis Ulrich (N. quadrata Ulrich, Il]. Geol. Surv., vol. viii, 1890). 
Of this genus we now know about fourteen species. Seven of these are from 
Trenton rocks, one (undescribed) from the Cincinnati and Hudson River groups, five 
from the Anticosti, and one, N. minuta Hall, sp., from the Niagara of Indiana. 
The genus differs conspicuously from the other generic types included in the 
Arthrostylide in having the zoarium continuous and dichotomously branched, the 
jointed character prevailing in the family being confined to the basal extremity. 
This part of the zoarium is, however, known of only one or two of the species, and 
it may yet be proven that in some of the species there is no basal articulation. But 
in the meantime, especially since the various forms agree very closely in zoccial 
features, we may assume that the lower extremity was pointed and articulated with 
a small basal expansion. The relations to Helopora, Hall, are therefore very nearly 
the same as between Hscharopora, Hall, and Arthropora, Ulrich. 
Nematopora ovauis Ulrich. 
PLATE III, FIGS. 24 and 25. 
Nematopora ovalis ULRICH, March, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 197. 
Nematopora quadrata ULnricu, Dec., 1890. Ill. Geo. Sury., vol. viii, p. 644. 
Original description: “Zoarium ramose; branches birfureating at intervals of 
about 2 mm., 0.5 to 0.4 mm. in diameter, subquadrangular or pentagonal in cross- 
section, each face with a row of zocecia. Zocecial apertures direct, very large, oval, 
nearly 0.8 mm. long by 0,15 mm, wide, enclosed by a sharply defined peristome, A 
