BRYOZOA. 209 
Phylloporina.] 
and Phyllopora, King, two genera that previous to 1885 were commonly employed in 
designating species of Phylloporina. The three genera agree in having similarly 
anastomosing zoaria, but the first belongs unquestionably to the Chilostomata, and is 
not known in rocks earlier than the Cretaceous. In the second the zoaria are short 
and constructed in every respect like those which characterize the Fenestellide. 
Phyllopora was not derived from the Lower Silurian Phylloporina, but from some 
type of Polypora subsequent to the extinction of the Silurian forms. Yet I am much 
inclined to believe that all three genera were derived successively from the same 
primal stock—not from each other—and that we have here merely a case illustrating 
the “tendency to variation in certain directions.” 
Compared with Drymotrypa, Ulrich, a genus beginning in the Trenton, and con- 
tinuing to the Lower Helderberg, the present genus is distinguished chiefly, perhaps 
solely, by the anastomosis of the branches, these being dichotomously branched and 
free in Drymotrypa. In the Carboniferous genus Chainodictyon, Foerste, the zocecia 
are somewhat shorter, and the back or “ reverse ” flatter and marked concentrically 
instead of longitudinally. 
PHYLLOPORINA SUBLAXA Ulrich. 
PLATE IV, FIGS. 1-7. 
Phylloporina sublaxa Uuricn, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 179. 
Zoarium an undulating flabelliform expansion, attaiming a diameter of 5 cm. or 
more, consisting of irregularly inosculating slender subcylindrical branches, varying 
in width from 0.3 to 0.6 mm., but averaging about 0.45 mm. Fenestrules large, sub- 
acutely elliptical, varying considerably in shape and size, generally two or three 
times longer than wide; measuring, longitudinally, the average number in 1 cm. is 
between five and six; transversely, nine or ten in the same space. These measure- 
ments apply to the Tennessee specimens. In the Minnesota form of this species the 
fenestrules are smaller, averaging between six and seven in | cm. lengthwise. 
Reverse of the Tennessee specimens strongly rounded, nearly smooth, or with faint 
longitudinal strie. In very young examples the latter would probably be more 
distinct. Figure 2 on plate IV represents an enlargement of the reverse of a small 
fragment obtained from the lower part of the limestone at Minneapolis, Minnesota, 
by splitting a block of limestone. As usual under such conditions the outer layer of 
sclerenchyma has adhered to the opposite side of the matrix and exposed a more 
youthful stage in the development of the zoarium, in which the reverse side was 
strongly striated. 
—14 
