BRYOZOA. 193 
Helopora.] 
Hetopora mucronata Ulrich. 
PLATE III, FIG. 10. 
Helopora mucronata ULRICH, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 192. 
Segments spine-like, slightly curved, 3.5 to 4.0 mm. long, tapering downward from 
the truncate upper end, where the diameter is 0.6 or 0.7 mm., to the acute and finely 
striated basal extremity. Zocecial apertures oblique, the inferior and lateral margins 
elevated, arranged longitudinally and spirally, with from six to eight forming a com- 
plete volution, and six in about 2.5 mm. lengthwise. Above each zocecial aperture 
two short striae. Obscure longitudinal ridges sometimes formed by the coalescence 
and continuance of the elevated lateral margins of the zocecial apertures. 
The curved and tapering form, the acute lower extremity, and the very slight 
development of the longitudinal ridges, distinguish this species from all the associ- 
ated jointed Bryozoa, as well as from //. divaricata and H. spiniformis. None of the 
other species of the genus are sufficiently near to require comparisons. 
Though readily distinguishable from all the known varieties of segments of the 
associated Arthroclema armatum, it may yet be shown by complete zoaria of the latter 
that /7. mucronata is but another form of segment of Arthroclema. Until such evi- 
dence is discovered we had best leave them as at present. 
Formation and locality.—Galena shales, near Cannon Falls, Minnesota, where it is associated with 
Helopora quadrata, Arthroclema armatum, and several species of Nematopara. Also at St. Paul. 
Mus. Reg. No. 8112. 
HELopora QUADRATA, 7. Sp. 
Fig. 10, Helopora quadrata Utricn. Galena shales, near Cannon Falls, Minnesota. a, basal par 
of a segment: b, the central portion of another, and ec, the upper extremity of a third, all x 18. 
Segments very slender, quadrate in cross-section, the angles sharp, the sides 
each about 0.28 mm. wide; entire length unknown, none of the segments at hand 
being complete, probably between 5 and 6 mm.; lower end bulbous, the upper with 
two flattened articulating faces. Zocecial apertures in four longitudinal rows, one 
on each of the concave sides; ovate, a little oblique, the inferior and lateral margins 
with a strong rim, produced backward, either straight or obliquely, as a sloping 
ridge. Zocecial apertures. separated by distances very nearly equal to their long 
diameter, with nine or ten in 3 mm. 
=e 
