136 THE PALEONTOLOGY OF MINNESOTA. 
- 3 [Rhinidictya. 
first of those species it differs mainly in its wider and nearly direct zocecial aper- 
tures and narrow interspaces, these being also without surface granulations so far 
as observed. Still, some of the Minnesota specimens referred here resemble R. 
nicholsoni more closely than do the Tennessee types. It is therefore not improbable 
that more detailed comparisons than I havé found time to make may show that, as 
I believed in 1886, R. nicholsoni also is represented in the Minnesota strata. F. grandis 
is readily distinguished by its wider branches and larger cells. . pediculata likewise 
seems Closely related, but.its peculiar growth and somewhat wider branches will, it 
is believed, serve to separate them. Lastly, Rk. fidelis so closely resembles this species 
in its external characters that Iam at a loss to point out really serviceable distin- 
guishing features. Asa rule the zowcial apertures of FR. trentonensis are a trifle nar- 
rower and less often of quadrate shape. Comparing their internal characters, we 
at once notice a decided difference in the inner part of the zocecia where that species 
presents a well developed superior hemiseptum. ‘This is a point of such importance 
that I am obliged to view the two species as widely distinct. 
Formation and locality—‘‘ Glade” limestone (Birdseye) at Lebanon, Tennessee; lower third of 
Trenton shales at Minneapolis, Minnesota. Rather rare. It has also been collected by Mr. C. Schuchert 
in the ‘‘ Lower Blue beds” at Janesville, Wisconsin, and Rockton, Illinois. 
Mus. Reg. Nos. 7549, 7560. 
RHINIDICTYA GRANDIS 1. Sp. 
PLATE V, FIGS. 11 and 12; PLATE VI, FIGS. 19 and 20. 
Zoarium bifolate, large, branchy, the branches Hattened, 2.5 to 3.5 mm. wide, the 
edges obtuse, with the non-poriferous margin of moderate width. Zocecia in from 
eleven to fifteen alternating rows, with large, almost direct, slightly oblong, hexa- 
gonal apertures, fourteen or fifteen in 5 mm. longitudinally, and nine of the central 
rows in 2mm. transversely. Interspaces thin, without papill, ridge-shaped, sloping 
down into the apertures from the summit, the latter reaching to about the same level 
in both the cross and longitudinal partitions. In conforming with the hexagonal 
shape and alternate arrangement of the zoccial apertures, the longitudinal walls 
usually take a decidedly zigzag direction. In the marginal rows the apertures are 
commonly more or less irregular in shape, size and arrangement. An occasional 
small cell may be noticed. 
In vertical sections the comparative erectness of the zocecia is to be noticed; 
also the shape of the walls, These show no sign of a superior hemiseptum, though 
a slight angularity is often perceptible at the turn into the vestibular region. 
