208 THE PALEONTOLOGY OF MINNESOTA. 
{Phylloporina. 
On the other hand, in P. aspera Hall, P. reticulata Hall, P. dawsoni Ulrich, and P. 
asperato-striata Hall, the zocecial tubes are shorter and thus approach the ordinary 
cryptostomatous cell more nearly. Indeed, P. dawsoni can be, I think, shown to be 
the first recognizable stage in the line of development that later on resulted in the 
highly diversified /enestellidw. This same species, however, and the remark applies 
with equal force to Drymotrypa dichotoma Ulrich, has much to remind us of Cyclosto- 
mata like Protocrisina, the zocecial orifice being but little constricted and the enclos- 
ing rim similarly prominent in all of them. 
We can show, therefore, apparent relations to three suborders of Bryozoa, and it 
becomes a question of some difficulty to decide where the family had best be placed. 
The Cryptostomata, however, seem best adapted to receive them, chiefly for the rea- 
son that the Phylloporinidw and Fenestellide are doubtlessly derived from the same 
stock, and the latter developed from the branch of the former mentioned. 
Genus PHYLLOPORINA, Ulrich. 
Retepora, as applied by various authors to Lower and Upper Silurian anastomosing Bryozoa (not 
Lamarck, 1801). 
Gorgonia ?, HALL, 1847, (not Gorgonia Linnzus, 1745). 
Intricaria, HALL, 1847; MILLER and Dyer, 1878, (not Defrance, 4823). 
Phyllopora (part.), ULRIcH, 1882. Jour. Cin. Soc. Nat. Hist., vol. v, p. 150. 
Nov. gen. (undesc.), ULRicu, 1886. Contri. to Amer. Pal., vol. i, No. 1, p. 5. 
Phylloporina, ULricn, 1890. Geol. Sury. Ill., vol. viii, pp. 399 and 639. 
Zoaria retiform, consisting of somewhat irregularly anastomosing, slender 
branches, with from two to eight ranges of zocecia on the obverse side. Reverse 
convex, longitudinally striated, without apertures. Zocecia tubular, often with the 
immature region very long, commonly with diaphragms. Apertures simple, uncon- 
stricted, rounded or subangular, generally with a peristome. Mesopores present, 
sometimes numerous, always closed at the surface; with diaphragms. Acan- 
thopores often present. 
Type: P. trentonensis (Retepora trentonensis Nicholson,* compare Letepora fene- 
strata Hall+). 
This genus includes some of the earliest types of Bryozoa known. Beginning in 
the Chazy with three closely related species, the genus continues in the Birdseye 
and Trenton with six or seven well-marked forms, four of which are described in the 
following pages. In the Cincinnati group we have two species, in the Clinton one, 
and in the Niagara one. The genus is not known from later deposits. 
The affimties and natural relations of the genus have already been touched 
upon in discussing the family. There remains to compare with Retepora, Imperato, 
*Geological Mag., vol. 2, p. 87, 1875. 
+Third Report N, Y. St. Mus. Nat. Hist., p. 178, 1850. 
