BRYOZOA. 211 
Phylloporina halli.] 
Obverse strongly convex, with three rather irregular rows of zoccia, their 
apertures subcircular, with a distinct peristome, about 0.1 mm. in diameter, eight 
or nine in 2 mm. Acanthopores abundant, irregularly distributed, rather large, 
especially so in the earliest forms of the species. Interspaces slightly concave, 
occasionally faintly pitted and striated. 
In tangential sections the zowcia are rather short, with a row on each side 
directed obliquely outward, and one series between them. The latter are wedge- 
shaped, and in deep sections appear as a more or less narrow central space. Dia- 
phragms, one in each tube, have been observed. 
None of the other Minnesota species of the genus are closely related. All of 
them are larger and stronger in both the branches and fenestrules. Nor are any of 
them found in the same beds with P. reticulata. 
Formation and locality.—Both the geological and geographical distribution of this species is 
extended. It was described originally from the Trenton limestone of New York, and in that position 
occurs also at many localities in Canada and Vermont, and at one or two points near Cannon Falls in 
Minnesota. In this state, however, a form occurs in the lower and middle thirds of the Trenton (Birdseye) 
shales at Minneapolis and St. Paul, that is indistinguishable. As yet it has not been found in the upper 
third of the shales, but, as stated, it reappears in the Galena shales (typical Trenton) near Cannon Falls. 
It is not improbable that P. clathrata (Intricaria clathrata Miller and Dyer), of the Cincinnati group of 
Ohio and Kentucky, is not specifically distinct from P. reticulata. At any rate I have so far failed to 
detect sufficient points of difference. 
Mus. Reg. No. 5955. 
PHYLLOPORINA HALLI Ulrich. 
PLATE IV, FIGS. 16-21. 
Phylloporina halli ULRicH, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 181. 
Original description: “Zoarium an undulating foliate expansion of unknown 
dimensions ; the largest fragment seen is 3.5 cm. in diameter ; thickness of strongest 
varying between 1.5 and 2.0 mm. Branches scarcely distinguishable as such, the 
zoarium having the appearance of a perforated plate rather than consisting of inos- 
culating branches. 
“Reverse with the fenestrules small, subcircular or oval, arranged more or less 
regularly in longitudinal and diagonal series, with from eight to ten in 1 cm. either 
way. When the arrangement is regular they are approximately of the same size, but 
when that is not the case some may be much smaller than the average. The latter 
are about 0.4 mm. in diameter. Over portions of old examples there may be a 
secondary deposit of sclerenchyma which occasionally fills the fenestrules com- 
pletely. Such deposits are, however, much less frequent than upon the celluliferous 
face. Branches convex, smooth, with an average width of 0.65 mm, Occasionally 
one may be swollen to twice that;width, 
