BRYOZOA. 173 
Phawnopora.] 
As shown in the accompanying cuts, the internal structure brought out in 
tangential sections is often almost exactly as in Ph. incipiens (plate XIII, fig. 17); 
other sections, however, in portions at least, show a structure more in accordance 
with fig. 7, plate XIII. 
It is evident that FH. (2) limitaris and E. confluens are varieties of one species, 
but because of their intermediate position between Escharopora and Phenopora, it 
is scarcely advisable to decide now which of the two names shall take the rank of a 
species, and which that of a variety. Such decisions should be deferred till we are 
better acquainted with the developmental history of fossil Bryozoa. 
Formation and locality —Not uncommon in the lowest third of the Trenton shales, at Minneapolis, 
Minnesota. Also in the middle third of the shales at the same locality, but less common and of more 
robust growth. A single specimen was observed among a lot of Bryozoa marking the lower shales, 
collected by Messrs. Schuchert and Scofield, near Preston, Minnesota. 
Mus. Reg. No. 5930. 
Genus PHASNOPORA, Hall. 
Phenopora, HAL, 1852, Pal. N. Y., vol. ii, p. 46; Utricu, 1882, Jour. Cin. Soc. Nat. Hist., vol. v. 
p. 152, and 1890, Geol. Sur. L1., vol. viii, p. 392; FOERSTE, 1887, Bull. 
Sci. Lab. Denison University, vol. ii, p. 157. 
Zoaria bifoliate, simple or branching, the base pointed and articulating into a 
small basal expansion, the same as in Ptilodictya and E’scharopora. Zocecial arrange- 
ment regular, in longitudinal, diagonally intersecting and transverse rows, with 
either the longitudinal or the diagonal series predominant. Two mesopores behind 
each zocecial aperture, one on each side, or one behind the other. Primitive cells 
elongate, commonly oblique or lozenge-shaped, at other times with the ends rectan- 
gular, always arranged between straight, longitudinal walls. Monticules, or mere 
clusters of large cells and mesopores, present when zoaria are wide enough. 
Type: Phenopora explanata Hall, 1852, Pal. N. Y., vol. ii, p. 46. 
From the above description it is obvious that the presence of the two mesopores 
is the only character to be relied upon in distinguishing the genus from Escharopora 
and Ptilodictya. The genus attains its highest development in the Clinton group, and 
in most of the species from that horizon the primitive cell has a peculiar oblique 
shape that is not seen in the Lower Silurian representatives of the genus, nor in any 
species of Escharopora, but is not uncommon among true Upper Silurian Ptilodictya. 
As might be expected, it is among the unbranched species that the greatest resem- 
blance to Ptilodictya obtains. Indeed, such species as Ph. ensiformis Hall, and Ph. 
lonsdalei (Ptilodictya lonsdalet Vine) are in every respect, save in this that they possess 
the characteristic mesopores, precisely like narrow species of Ptilodictya. 
In the following classification I have arranged the species in sections the same 
as under Escharopora. Except in one instance, I have not been able to obtain 
